International Classification of Diseases and Related Health Problems - 11 (KLASIFIKASI INTERNASIONAL UNTUK PENYAKIT DAN MASALAH KESEHATAN YANG BERHUBUNGAN)

1 Part 1 - An Introduction to ICD-11

1.1 Purpose and multiple uses of ICD

The International Classification of Diseases and Related Health Problems (ICD) is a tool for recording, reporting and grouping conditions and factors that influence health. It contains categories for diseases, health related conditions, and external causes of illness or death. The purpose of the ICD is to allow the systematic recording, analysis, interpretation and comparison of mortality and morbidity data collected in different countries or areas and at different times. The ICD is used to translate diagnoses of diseases and other health problems into an alphanumeric code, which allows storage, retrieval, and analysis of the data. The ICD has become the international standard diagnostic classification for all general epidemiological and many health management purposes. These include analysis of general health situations of population groups, monitoring of incidence and prevalence of diseases, and other health problems in relation to other variables, such as the characteristics and circumstances of the affected individuals. ICD is also suitable for studies of financial aspects of a health system, such as billing or resource allocation.

The ICD has evolved over the past 150 years from an International List of Causes of Death to a comprehensive classification system for use in mortality, morbidity, casemix, quality measurement and patient safety. It can be used in primary care, secondary care, and research. The ICD is used to allocate the majority of global health resources. Users of the ICD include physicians, nurses, other health care providers, researchers, health information management professionals, coders, health information technology workers, analysts, policy-makers, insurers, patient organisations, and many more.

The ICD is used in various settings with different levels of resolution ranging from a set of 100 codes to more than 10,000 codes. It therefore includes an information framework that contains a fully specified set of health concepts and their characteristics and relationships. The ICD–11 ensures consistency with traditional use cases of earlier ICD versions, because it has been built with the past revisions in mind. Past data analyses based on older versions of ICD can be linked to analyses of data based on ICD–11.

All World Health Organization (WHO) Member States are expected to use the most current version of the ICD for reporting death and illness (according to an international treaty, the ‘WHO Nomenclature Regulations’, adopted by the World Health Assembly in 1967). ICD–10 has been translated into 43 languages, and ICD–11 has been available in all 6 official languages since its publication (English, French, Spanish, Russian, Chinese, Arabic). Most countries (115 in 2017) use the system to report mortality data, a primary indicator of health status.

The ICD is primarily designed for the classification of diseases and injuries. However, not every problem or reason for coming into contact with health services can be categorized in this way. Consequently, the ICD includes a wide variety of signs, symptoms, abnormal findings, complaints and social factors that represent the content from health-related records (see section on morbidity). The ICD can therefore be used to classify data recorded under headings such as ‘Diagnosis’, ‘Reason for admission’, ‘Conditions treated’ and ‘Reason for consultation’, which appear on a wide variety of health records from which statistics are derived, for treatment, prevention, or patient safety.

 

1.1.1 Intended use

The ICD has been designed to address the needs of a broad range of use cases: Mortality, morbidity, epidemiology, casemix, quality and safety, primary care. Detailed information on the different use cases is available in other sections for mortality use and different morbidity uses. A situation may arise, which anticipates using the ICD-11 for a purpose for which it has not been designed. In this situation, the categorization used within the ICD-11 and its additional features may not be able to address such a new use case. In such cases, it is recommended to consult with the WHO to ensure that the information collected is appropriate to the intended new use.

1.1.2 Classification

A classification is ‘an exhaustive set of mutually exclusive categories to aggregate data at a pre- prescribed level of specialization for a specific purpose’ (ISO 17115). Classification involves the categorization of relevant concepts for the purposes of systematic recording or analysis. The categorization is based on one or more logical rules. The purpose of a health classification varies. For example, it may be used in the analysis of cause of death (mortality), morbidity, activity limitation, or participation restriction. Low frequency concepts tend to be grouped but rare concepts may be individually classified if necessary. Coding rules must be incorporated in the classification to achieve consistency of coding and comparability of coded data over time and space. Classifications are complementary to terminologies, since they are designed to be used for standardised coding of information for statistical purposes.

FIC)

The WHO Family of International Classifications (WHO-FIC) comprises classifications that have been endorsed by the WHO to describe various aspects of health and the health system in a consistent manner.

The WHO-FIC provides standardised building blocks for health information systems and consists of three broad groups: Reference classifications, Derived classifications, and Related classifications.

The Reference and the Derived classifications are based on the Foundation Component, which is a large collection of terms and their relationships, which describe health and health related domains.

Terms related to diseases and health related problems are organised into the ICD, those pertaining to functioning into the ICF, and those related to interventions into ICHI (International Classification of Health Interventions). Terms from the Foundation Component may be used in more than one Reference classification.

Derived Statistical Classifications and Tabulations (‘derived classifications’) draw on terms that may come from one or more of the Reference classifications. Within the WHO-FIC Family, Related classifications are regarded as complementary to the Reference and Derived classifications. Related classifications have their own sets of terms, but can also share terms as part of the WHO-FIC Family. For example, the International Classification of Nursing Practice (ICNP), a related classification in the Family, draws on terms from the Foundation Component in the same way that the reference and derived classifications draw on terms from the Foundation Component. ICNP also uses terms specific to nursing practice which are not found in the Foundation Component, but which may be included in the future.

WHO-FIC Family

Figure 1: Relationships between the WHO Family of International Classifications and related classification, the Foundation Component, and shared terminologies.

The purpose of the WHO-FIC is to assist the development of reliable statistical systems at local, national, and international levels, with the aim of improving health status and health care. The classifications are the property of the WHO or other groups. Health related information might sometimes require additional detail to that contained in the ICD. A group or ‘family’ of health relevant classifications covers these needs both by classification of domains different from those of the ICD and provision of more detail for specific uses, e.g. cancer registration. The WHO-FIC designates a suite of integrated classification products that share similar features and can be used singularly or jointly to provide information on different aspects of health and health care systems. For example, the ICD as a reference classification is mainly used to capture mortality and morbidity. Functioning is classified in the International Classification of Functioning, Disability and Health (ICF) and health interventions in the International Classification of Health Interventions (ICHI).

In general, the WHO-FIC aims to provide a conceptual framework of information dimensions which are related to health and health management. In this way, it provides a common language that improves communication and permits comparisons of data within countries, across countries, health care disciplines, services, and time. The WHO and the WHO-FIC Network (including Collaborating Centres, Non-Governmental Organisations, and selected experts) strive to build the family of classifications based on sound scientific and taxonomic principles, ensure that it is culturally appropriate and internationally applicable, and meet the needs of its different users by focusing on the multi-dimensional aspects of health.

1.1.4 WHO-FIC: Reference Classifications

Reference classifications cover the main parameters of the health system, such as death and disease (ICD), disability, functioning, and health (ICF) and health interventions (ICHI). WHO-FIC reference classifications are a product of international agreements. They have achieved broad acceptance and official agreement for use and are approved and recommended as guidelines for international reporting on health. They may be used as models for the development or revision of other classifications. The three Reference classifications are:

1. International Classification of Diseases and Health Related Problems (ICD)
2. International Classification of Functioning, Disability & Health (ICF)
3. International Classification Health Intervention (ICHI)

1.1.4.1 Disability and Functioning – ICF

The ICF is the WHO’s framework for measuring health and functioning/disability at both the individual and population levels. While the ICD classifies diseases and causes of death, the ICF classifies health domains. ICD and ICF together provide tools to capture the full picture of health.

The ICF classifies health and health-related states in two parts. Part one addresses functioning and disability, described from the perspectives of the body, the individual, and society, and is composed of two components: Body Functions and Structures and Activities and Participation life areas. Part two covers contextual factors and has two components: Environmental Factors and Personal Factors (currently not classified in ICF), since an individual’s functioning occurs in a context.

Functioning is a generic term for body functions (e.g. memory), body structures (e.g. occipital lobe), and activities and participation life areas (e.g. walking, engaging in paid work). It denotes the neutral aspects of the interaction between an individual (related to the individual’s health) and that individual’s contextual factors (environmental and personal factors).

Disability is an umbrella term for impairments, activity limitations and participation restrictions. It denotes the negative aspects of the interaction between an individual (with a health condition) and that individual’s contextual factors (environmental and personal factors). Disabilities are envisioned as a continuum and therefore the ICF and the codes within it do not confer an international binary status of disabled/not disabled. Levels of disability can be used descriptively in clinical settings when formulating a case. Program and policy decision-makers can apply the ICF and specify their own standards for the level of disability as eligibility criteria that are relevant for specific purposes.

ICF includes the following other descriptions:

• Body functions are the physiological functions of body systems (including psychological functions).
• Body structures are anatomical parts of the body such as organs, limbs and their components.
• Impairments are problems in body function or structure such as a significant deviation or loss.
• Activity is the execution of a task or action by an individual.
• Activity limitations are difficulties an individual may have in executing activities.
• Participation is involvement in a life situation.
• Participation restrictions are problems an individual may experience in involvement in life situations.
• Environmental factors make up the physical, social and attitudinal environment in which people live and conduct their lives.

ICF includes codes for Body Functions (b), Body Structures (s), Activities and Participation (d), and Environmental Factors (e).

ICF codes are only complete with the presence of a qualifier, which denotes the level of health (i.e. severity of the problem from ‘no problem’ to ‘complete problem’). Without qualifiers, codes have no inherent meaning. The ICF acknowledges that every human being can experience a decrement in health and thereby experience some disability. Disabilities can be temporary and may be brief (such as staying home from work for a few days with the flu); they can also be chronic or permanent and may fluctuate in severity over time.

1.1.4.2 Interventions – ICHI

Intervention classifications are designed to include all kinds of health interventions for treatment, diagnosis, or prevention. The International Classification of Health Interventions (ICHI) includes interventions across all functional sectors of the health system, covering acute care, primary care, rehabilitation, assistance with functioning, prevention, public health, and ancillary services. Interventions provided by all types of providers have been included. The importance of describing and classifying health interventions has long been understood. An International Classification of Procedures in Medicine (ICPM) was published by WHO in 1978 but was not maintained. ICHI is much broader than the former ICPM because it includes the full range of health interventions. Development of ICHI began in 2007, as a joint effort of the WHO- FIC Network and WHO. Its structure has been completed, an alpha version published in 2012 and a beta version in 2015. Finalisation is planned for 2019.

Table 1: Descriptions and terms used in creation of ICHI classifications.

Axes	Inclusions	Example
The Target axis contains the entities on which the action is carried out.	Anatomy, Human function, Person or client, Group or population
The Action axis is defined as a deed which is done by an actor to a target during a health care intervention.	Investigation, Treating, Managing, Informing, Assisting, Preventing
The Means axis contains the entities describing the processes and methods by which the action is carried out.	Approach: the process by which the target of the action is accessed	open, endoscopic
	Technique used as part of the action	radiation, magnetic resonance
	Method describing how the action is undertaken	law enforcement, method of transport.

Other attributes of interventions are included as ‘Means’ in the ICHI Content Model. The content of the axes has been restricted to attributes that are common to many interventions. In particular:

• Devices have not been included as an axis because most interventions do not involve a device and devices change rapidly
• Drugs or other substances administered through an intervention are classified elsewhere (ICD, The Anatomical Therapeutic Chemical Classification with Defined Daily Doses (ATC/DDD), INN).

The coding system comprises a 7-character category structure for the three axes:

• Three letters for the Target
• Two letters for the Action
• Two letters for the Means

ICHI is a flat file comprising valid 7 letter combinations of the three axes. For each intervention included in ICHI, the appropriate 7 letter combination is identified. Not every possible combination of the three axes represents a valid ICHI domain.

1.1.4.3 WHO-FIC: Derived Classifications

Derived classifications are often tailored for use at the national or international level or for use in a particular specialty. Derived classifications are based upon reference classifications (ICD, ICF, ICHI). Derived classifications may be prepared by: - adopting the reference classification structure and classes - providing additional detail beyond that provided by the reference classification, or through rearrangement or by aggregation of items from one or more reference classifications.

ICD-11 has specialty linearizations that are derived from the common foundation. These include a version for dermatology, one for primary care and one for mental health. Others may follow.

1.1.4.4 Related Classifications

Related classifications are included in WHO-FIC to describe important aspects of health or the health system not covered by reference or derived classifications. Related classifications are:

• International Classification of Primary Care (ICPC)
• International Classification of External Causes of Injury (ICECI)
• Technical aids for persons with disabilities (ISO9999)
• The Anatomical Therapeutic Chemical Classification with Defined Daily Doses (ATC/DDD)
• The International Classification for Nursing Practice (ICNP)

 

1.1.5 ICD Use in health information systems

Health information systems include a range of different components for collection, analysis, and use of the data. Information sources could for example be population-based, health facility- based, or focused on particular diseases. The main population-based sources of health information are census data, household surveys, and vital registration systems.

Health facility-related data sources include public health surveillance, health services data (that may be referred to as health management information systems or routine health information systems), and health system monitoring data (e.g. human resources, health infrastructure, financing).

National health accounts are designed to provide a comprehensive picture of health financing. Coding enables the recording of health information in a language independent way. Standardization of coding enables both intra- and international data comparison. For example, ICD coded data can be compared across different sectors of the health system – if the same coding rules are applied.

Health information systems are increasingly based on digital (electronic) reporting and coding. ICD–11 is designed to be used in such environments. In many places information collection is based on paper reporting in a traditional analogue way. ICD–11 can be produced in a printed version for use in paper based systems.

1.1.5.1 Use of ICD–11 in a digital setting and web services

The ICD-11 is used for coding of diagnoses, in electronic health records or electronic death certificates, or in other places. Special tools facilitate finding specific ICD-11 codes for any of the several dimensions that define an ICD-11 entity or category. Additional detail can be added using multiple codes for one condition. Retaining the unique identifier of the coded ICD-11 entity allows the same information to be reused across different translations. WHO has developed the ICD web services (https://icd.who.int/icdapi); designed to support interoperable machine-to-machine interaction.

1.1.5.2 Use of ICD–11 in an analog paper-based setting

The ICD-11 is used as analogue printed version in some countries. Information is reported on paper version and then coded with the ICD-11. It should be noted that paper-based recording requires manual transcription of the information into electronic systems and should be substituted by electronic reporting as early as possible in the information chain. Further problems with paper-based recording include readability and timeliness. ICD-11 supports many ways of computer assisted coding including sanctioning of code combinations and other possible plausibility checks. The long term goal for all users should be coding of ICD-11 in an electronic environment.

In the print version, the information is divided into 3 volumes, the tabular list, the reference guide, and the index. All three are needed to use the ICD correctly.

1.1.5.3 Electronic version

In the browser version of the ICD, most information is interlinked and visible in the relevant context. The WHO provides this version for browsing ICD-11 in multiple languages (linked from https://icd.who.int). This tool allows the user to retrieve concepts by searching terms, anatomy or any other element of the content model. With this browser, users can also contribute to the updating and continuous improvement of ICD with comments and solutions. Such input is reviewed for consideration for inclusion on an annual basis.

ICD–11 can also be accessed using web services with user specific software. The IT guide to the ICD provides more details on compatibility requirements: https://icd.who.int/icdapi. Both the web services and the online browser allow access to all Tabular lists of the ICD, for mortality and morbidity statistics, primary care, or for a specialty linearization for certain specialized domains.

1.1.6 Links with other Classifications and Terminologies

ICD coded entities or categories can be used in conjunction with other health relevant classifications or terminologies to fully document an episode of care, or a case for research.

1.1.6.1 Integrated use with Terminologies

Classification involves grouping information according to logical rules. Terminology allows the reporting of information at any desired level of detail: for example, body parts, findings, or other elements that constitute a disease. Only items defined in a terminology can be reported on (i.e. Terminologies have no mechanism to report new information that has not previously been added to the terminology). In contrast, a classification has residual classes (‘other specified’ or ‘unspecified’) that ensures that all cases can always be classified. In a terminology, as much as in a modern disease classification, a disease can be defined, for example by establishing linkages between its elements, such as anatomy or findings. Terminologies retain the information without emphasizing any aspect of the recorded information.

In contrast, classifications allow for identification of ‘relevant parts’ of the content, for example, for public health. International agreement about these relevant parts makes sure that the aggregated information is internationally comparable. The standardised use of the aggregation logic of a classification and the standardised use of the detailed information of a terminology aim at the same result: comparability. International agreement processes are necessary in both cases – and must be the same as soon as the same question has to be answered by the aggregation/classification.

Terminologies and classifications should be considered complementary. The Systematized Nomenclature of Medicine Clinical Terms (SNOMED CT) is an example for a linked terminology within ICD-11. The information coded through SNOMED CT can be categorized with ICD. Additional terminologies include for example ICD-O, INN or ICECI.

1.1.6.2 Functioning in ICD and joint use with ICF

Historically, the ICD has used certain disability concepts as common disease or disorder entities, such as: Blindness, Deafness, Mental Retardation, Learning Disability, or Paraplegia, as well as certain disability concepts for other purposes, such as ‘disability as a sequela of injury’, and ‘limitation of activities due to disability’. The ICF was developed after the publication of ICD–10. The ICD–11 has been created both to share concepts and be used jointly with the ICF. This partnership may assist with the following tasks:

• evaluation for general medical practice (e.g. fitness for work)
• evaluation for social benefits (e.g. disability, pension)
• payment or reimbursement purposes
• needs assessment (e.g. for rehabilitation, occupational assistance, long term care.)
• outcome evaluation of interventions

Signs and symptoms in the ICD are aligned with body functions in the ICF, and ‘factors influencing health status’ in the ICD align with contextual factors in the ICF.

Additional selected ICF categories are drawn from the component activities and participation and help to describe the functional limitations commonly associated with the specific health conditions in a functioning pattern. The impact of the disease or disorder in the daily activities of a person may vary depending on the severity of the condition as well as the contextual factors (e.g. environmental factors) and possible co- morbidities. The ICD takes an approach that identifies ‘severity’ as a property of the disease/disorder and describes the impact of the health condition on the daily life of a person as a functioning set.

The functioning section that is embedded in ICD serves to generate a summary functioning score based on assessment of the individual. The set of functioning items in ICD-11 allows the WHO Disability Assessment Scale (WHODAS), and the Model Disability Survey (MDS, module 4000, Functioning) to be used to generate the summary score. Wherever full functioning reporting is desired, the ICF should be used.

 

1.2 Structure and taxonomy of the ICD Classification System

The chapter and block structure of the ICD has evolved in 11 iterations over 100 years. The authoring of ICD follows a set of rules that ensure the functional and structural integrity of the classification. The evolution of ICD carefully balances the need for categories that match current knowledge while allowing statistical comparability over space and time.

The chapter structure of ICD reflects major aspects of diseases. Chapters are not intended to delimit areas of medical expertise or domains of specialties. The link to any specialty or reimbursement schemes is secondary. In particular, reimbursement schemes can be easily adapted. The ICD has categories for diseases, disorders, syndromes, signs, symptoms, findings, injuries, external causes of morbidity and mortality, factors influencing health status, reasons for encounter of the health system, and traditional medicine. ICD-11 complements these categories with additional detail such as anatomy, substances, infectious agents, or place of injury. ICD-11 also comes with a set of rules and explanations for its use, required reporting formats, and necessary metadata.

The most widespread use of ICD over time and geographically is for cause of death statistics. ICD is also used for classification of clinical documentation, to provide standardised, language independent information for morbidity use, such as resource allocation, casemix, patient safety and quality of care, as well as primary care and research. ICD and its descriptions are also used as a framework in legislation.

 

1.2.1 Taxonomy

After death statistics, the second most important use of ICD is classification of clinical documentation to provide pertinent information for resource allocation, casemix, patient safety and quality of care as well as primary care and other kinds of statistics. A statistical classification of diseases must be confined to a limited number of mutually exclusive categories able to encompass the complete range of morbid conditions. The categories are chosen to facilitate the statistical study of disease phenomena. Every disease or morbid condition must have a well-defined place in the list of categories. Consequently, throughout the classification, there will be residual categories for other and miscellaneous conditions that cannot be allocated to the more specific categories. The following measures apply in determining whether an entity qualifies to become a unique category:

1. Epidemiological evidence: frequency analyses of coded mortality and morbidity data
2. Clinical evidence: disease evidence provided by the medical specialties
3. Granularity: minimum detail reported and useful in mortality (mortality data) or primary care
4. Continuity: preserve the level of detail pre-existing in ICD
5. Parsimony: the need to limit the number of categories for international mandatory reporting

A statistical classification can allow for different levels of detail if it has a hierarchical structure and subdivisions. A statistical classification of diseases should retain the ability both to identify specific disease entities and to allow statistical presentation of data for broader groups, to enable the attainment of useful and understandable information. The same general principles apply to the classification of other health problems and reasons for contact with health-care services, which are also incorporated in the ICD. The ICD has developed as a practical, rather than a purely theoretical classification, in which there are a number of compromises between classification based on aetiology, anatomical site, circumstances of onset, or other criteria.

ICD-11 draws extensively on the method of combining several codes to describe a clinical condition to the desired level of detail. Its electronic architecture allows assignment of unique identifiers to any condition listed - independently whether the condition is grouped in a statistical class or whether it represents a class of its own. The two approaches together allow the option of keeping coding simple where diagnostic detail is limited; and the alternative to add detail where diagnostic reporting requires a high level of sophistication.

1.2.2 Chapter structure

The ICD is a variable-axis classification. The structure has developed out of that proposed by William Farr in the early days of international discussions on classification structure: epidemic diseases, constitutional or general diseases, local diseases arranged by site, developmental diseases, injuries.

These groups remain in the chapters of ICD–11. The structure has stood the test of time and, though in some ways arbitrary, is still regarded as more useful for general epidemiological purposes than any of the alternatives tested. The conservation of the structure acknowledges the need for stability while allowing incorporation of additional sections.

The special groups bring together conditions that would be inconveniently arranged for epidemiological study were they to be scattered, for instance in a classification arranged primarily by anatomical site. These conditions formulate the ‘special groups’ chapters:

Chapter	Title
1	Certain infectious or parasitic diseases
2	Neoplasms
3	Diseases of the blood or blood-forming organs
4	Diseases of the immune system
18	Pregnancy, childbirth, or the puerperium
19	Certain conditions originating in the perinatal period
20	Developmental anomalies
22	Injury, poisoning or certain other consequences of external cause

The distinction between the ‘special groups’ chapters and the ‘body systems’ chapters has practical implications for understanding the structure of the classification, for coding to it, and for interpreting statistics based on it. It has to be remembered that, in general, conditions are primarily classified to one of the ‘special groups’ chapters.

Where there is any doubt as to where a condition should be positioned, the ‘special groups’ chapters should take priority. This principle is enforced in the ‘excludes’ notes at the beginning of each chapter in the ICD. For example, cervical dysplasia grade 1 is coded to Chapter 2 ‘Neoplasms’ because distinction between dysplasia and neoplasia and clinical management are subject to a set of recommended criteria that may change over time.

1.2.3 Revision major steps

The revision of ICD-11 has taken place in several phases. First, a list of issues that were known from the use of ICD-10 and that could not be solved in its classification structure was compiled and possible solutions were formulated.

Second, input was received from many scientific groups in the key subject areas with a focus on the clinical perspective.

Finally, centralised editing occurred, aimed to adjust imbalances in content generated by multiple, independently operating expert groups in the previous phase of the revision, and to ensure the overall structure is consistent and practicable for users in mortality and morbidity statistics. The final version also received input from field testing, Member State comments, and ongoing submission and processing of proposals.

1.2.4 General features of ICD-11

The main structural innovation of ICD–11 is that it is built on a Foundation Component from which the tabular list (the statistical classification for morbidity and mortality) can be derived.

Table 1: ICD-11 Terminology

ICD-11 Term	Explanation
Foundation component	Underlying data base content that holds all necessary information to generate print versions of the tabular list and the alphabetical index, as well as additional information that is needed to generate specialty linearizations of ICD-11 and country specific modifications.
Stem code	Stem codes are codes that can be used alone. They are found in the tabular list of ICD-11 for Mortality and Morbidity Statistics. Stem codes may be entities or groupings of high relevance, or clinical conditions that should always be described as one single category. The design of stem codes makes sure that in use cases that require only one code per case, a meaningful minimum of information is collected.
Extension code	Extension codes are designed to standardise the way additional information is added to a stem code when users and settings are interested in reporting more detail than is included in a stem code. Extension codes can never be used without a stem code and can never appear in the first position in a cluster.
Precoordination	Stem codes may contain all pertinent information about a clinical concept in a pre-combined fashion. This is referred to as ‘precoordination’.
	Example: BD50.40 Abdominal aortic aneurysm with perforation
	Example: CA40.04 Pneumonia due to Mycoplasma pneumoniae
Postcoordination	Postcoordination refers to linking (through cluster coding) multiple codes (i.e. stem codes and/or extension codes) together, to fully describe a documented clinical concept.
Cluster coding	Cluster coding refers to a convention used (either forward slash (/) or ampersand (&)) to show more than one code used together (e.g. stem code/stem code(s)&extension code(s)) to describe a documented clinical concept.
	Example: Diagnosis: Duodenal ulcer with acute haemorrhage, Cluster: DA63.Z/ME24.90; Condition - DA63 Duodenal ulcer, unspecified; Has manifestation (use additional code, if desired) - ME24.90 Acute gastrointestinal bleeding, not elsewhere classified
Primary and secondary parents	The hierarchy of ICD-11 is defined the same as it was in previous versions of ICD. The possibility to connect specific diseases and concepts within the classification to another parent code was introduced to enable specific extracts of the Tabular list for medical specialties or for specific use cases.
	Example: A code for a malignant neoplasm of the skin is in the chapter for malignant neoplasms. The primary parent for this code is a code or a block from this chapter. However, a medical doctor treating only skin diseases might want to see only codes from the classification that are relevant for his or her specific clinical purpose. Therefore, a secondary parent was defined in the skin chapter which will only show the code in this chapter if the specific extract of code for his or her use case is selected.

1.2.4.1 Coding scheme

• The coding scheme always has a letter in the second position to differentiate from the codes of ICD–10.
• In ICD–11, the first character of the code always relates to the chapter number. It may be a number or a letter. The code range of a single chapter always has the same character in the first position.
• In order to describe a causal relationship between conditions in a code title the preferred term is ‘due to’.
• In order to indicate the concurrence of two conditions in a code title the preferred term is ‘associated with’.

The codes of the ICD–11 are alphanumeric and cover the range from 1A00.00 to ZZ9Z.ZZ. Codes starting with ‘X’ indicate an extension code (see Extension codes). The inclusion of a forced number at the 3rd character position prevents spelling ‘undesirable words’. The letters ‘O’ and ‘I’ are omitted to prevent confusion with the numbers ‘0’ and ‘1’. Chapters are indicated by the first character. For example, 1A00 is a code in Chapter 1, and BA00 is a code in Chapter 11.

1.2.4.2 Extension codes

ICD–11 allows for adding specific detail to coded entities using the following mechanisms:

1.      The extension codes comprised of groups of codes e.g. anatomy, agent, histopathology and other aspects that may be used to add detail to a stem code. Extension codes are not to be used alone but must be added to a stem code. Not all extension codes can be used with every stem code.

2.      ‘Code also’ instructions provide additional aetiological information which is mandatory to code in conjunction with certain categories, because that additional information is relevant for primary tabulation. The ‘code also’ instruction marks the categories that must be used in conjunction with the indicated condition. In some instances, they may be a reason for treatment in their own right, where aetiology is unknown.

3.      ICD–11 has an explicit way of marking codes that are postcoordinated to describe one condition, called cluster coding. This is a notable new feature in ICD-11 that creates an ability to link core diagnostic concepts (i.e. stem code concepts) when desired, and/or to add clinical concepts captured in extension codes to primary stem code concepts. Either way, it should be emphasized that the clustering ability inherent to ICD-11 is one of the significant changes relative to ICD-10.

1.2.4.3 Other general features

ICD–11 categories have short and long descriptions labelled ‘additional information’. The short description is a maximum of 100 words on the entity that states things that are always true about a disease or condition and necessary to understand the scope of the rubric. It appears in the tabular list of the classification. The long ‘additional information’ is the full description, without length restriction.

·         Special tabulation lists continue to exist in ICD-11, but there are three additional lists - the Startup Mortality List (SMoL), the list for verbal autopsy, and the list for infectious diseases by agent. Specialty linearizations allow the representation of content from the angle of a specialty, such as dermatology or neurology, creating subsets, and allowing the pre-coordination of more detail, if desired.

·         For morbidity, the definition of main condition has changed to be the condition that is determined to be the reason for admission, established at the end of the stay. This definition is less prone to interpretation, and countries that had switched from the ‘most resource intensive’ definition to the ‘reason for admission established at the end of the stay’ using ICD-10, noticed only small changes in their activity statistics.

1.2.5 Foundation Component and Tabular Lists of ICD–11

The Foundation Component is a multidimensional collection of all ICD entities. Entities can be diseases, disorders, injuries, external causes, signs and symptoms. Some entities may be very broad, for example ‘injury of the arm’, while others are more detailed, for example ‘laceration of the skin of the thumb’. The Foundation Component also has the necessary information to use the entities to build a tabular list. The Foundation Component includes information on where and how a certain entity is represented in a tabular list, whether it becomes a grouping, a category with a stem code, or whether it is mentioned as an inclusion term in a particular category.

Several different tabular lists can be built from the Foundation Component. Drawing on the same Foundation Component, a set of tabular lists that builds on the same hierarchical tree can be created – a set of so called congruent tabular lists. The Foundation Component includes instructions on how to combine certain codes in a tabular list to achieve more detail in coding. These rules help coders and computer systems to visualize the permitted code combinations when they are using a tabular list.

In a tabular list, entities of the Foundation Component become categories. The categories are mutually exclusive and jointly exhaustive and linked to a mono hierarchical tree (they have only one parent). The information related to an entity that has become a category and has multiple parents is still available from the Foundation Component. This information can be used to visualize that category in more than one place in the tabular list, e.g. showing them in black font in its place for reference tabulation and in grey font in any other place for browsing or alternative tabulations. ICD–11 has multiple congruent tabular lists with varying levels of detail.

1.2.5.1 Precoordination and Postcoordination, Cluster coding

A health condition may be described to any level of detail, by applying more than one code, or by ‘postcoordinating’ (i.e. combining):

• two or more stem codes, (i.e. code1/code2)
• stem codes with one or more extension codes. (i.e. stem code & extension code1 & extension code2)

In this manner, the classification can address a large number of clinical concepts with a limited range of categories.

Stem codes contain all pertinent information in a pre-combined fashion. This is referred to as ‘precoordination’. When additional detail that pertains to a condition is described by combining multiple codes, this is referred to as ‘postcoordination’. The mechanism of showing that codes are postcoordinated is called cluster coding in ICD-11.

Example

Precoordination of concepts in a single code

Condition: 2C25.2 Squamous cell carcinoma of bronchus or lung.

In precoordination, both site and pathology are combined in a single precoordinated stem code.

Example

Postcoordination of concepts combined through cluster coding

In postcoordination, the condition urinary tract infection due to Extended spectrum beta-lactamase producing Escherichia coli’ is expressed through a combination of two linked or clustered stem codes.

Condition: GC08.0 Urinary tract infection, site not specified, due to Escherichia coli

Has manifestation (use additional code, if desired): MG50.27 Extended-spectrum beta-lactamase producing Escherichia coli

Cluster code: GC08.0/MG50.27

1.2.5.2 Multiple Parenting

An entity may be correctly classified in two different places, e.g. by site or by aetiology. For a disease like oesophageal cancer this would mean that it could be classified to cancers (malignant neoplasms) or to conditions of the digestive system. In the same way, cerebral ischaemic conditions could be classified to the vascular system – where the problem arises - or to the nervous system – where the ischaemia impacts and manifests with symptoms.

1.2.6 Language independent ICD entities

ICD-11 entities are language independent. All entities have uniform resource indicator (URI), and have a specific place in a hierarchy of groups, categories, and narrower terms. The maintenance of the ICD-11 on an international level is handled in the English language but the content model of ICD–11 is language independent and allows binding of any desired language to the elements of its Foundation Component. In this way, an international translation base facilitates translations or multilingual browsing.

1.2.7 Organisation of a Congruent System

Many countries use a single coding system (tabular list) for all use cases. Congruent, telescopically expandable and collapsible purpose-independent subsets for morbidity coding in different settings (comparable to Verbal Autopsy, or initial implementation lists for mortality) allow gathering of information at different levels of detail and still allow for comparison of the collected information at the level of the common description.

1.3 Main Uses of the ICD: Mortality

Mortality statistics are widely used for medical research, monitoring of public health, evaluating health interventions, and planning and follow-up of health care. Rules adopted by the World Health Assembly regarding the selection of a single cause or condition, from death certificates, for routine tabulation of mortality statistics are provided to standardise production of mortality data. Implementation of the ICD for mortality requires setting up an infrastructure for reporting and storing information, designing information flows, quality assurance and feedback, and training for classification users working with the input or output of data.

1.4 Main Uses of the ICD: Morbidity

Morbidity data are used for statistical reporting mostly at national or local levels. While some of this statistical reporting is conducted within an academic research context, it is commonly conducted in applied settings to inform health system and public health agency decision- making. ICD coded data also forms the basis of different casemix systems, such as different varieties of Diagnosis Related Groups (DRGs). Coded morbidity data can also be used to inform a variety of clinical guidelines through provision of Foundation Component information on burden of disease.

1.4.1 What is coded: Conditions of patient

The health care practitioner responsible for the patient’s treatment is also responsible for documenting the patient’s health conditions. This information should be organised systematically by using standard recording methods. A properly completed record is essential for good patient management. It is also an essential prerequisite to the creation of a valid coded record of patient diagnoses, derived through a coding process from written information describing a patient’s medical condition. When a sound written record of patient conditions is available, successful coding of this information in ICD and associated classifications produces a valuable source of epidemiological and other statistical data on morbidity and other health care problems. The person transforming the information on the stated condition to codes (the ‘coder’) may be the health care practitioner or a clinical coder (who is not responsible for the patient’s treatment). In the latter situation, which is quite common among member countries, the coder depends on the adequacy of clinical documentation of patient conditions by health care practitioners in the medical record. The primary importance of clinical documentation by health care practitioners as the starting point for coded health data cannot be overstated, and needs to be underlined as being a matter of key importance within countries and internationally – with implications for health information and clinical documentation teaching within health care practitioner training programs.

1.5 Traditional Medicine

Traditional Medicine (TM) is an integral part of health services provided in many countries. International standardization by including Traditional Medicine within the ICD allows for measuring, counting, comparing, formulating questions and monitoring over time. Although some of these countries have had national classification systems for many years, information from such systems has not been standardised or available globally.

It is recommended that coding of cases with ICD-11’s chapter on Traditional Medicine disorders and patterns (TM1) be used in conjunction with the Western Medicine concepts of ICD Chapters 1-25. Such integration will bring community benefit and enable issues such as safety and efficacy of treatments for different conditions to be established. The Traditional Medicine (TM1) chapter can also be used alone.

1.6 ICD maintenance and application

The ICD maintenance process allows the updating of the ICD following the evolution in the understanding of diseases, treatments, and prevention. It also ensures improvements and clarifications coming from daily use of ICD, and requests by Member States. A proposal and review mechanism on the online platform makes the process transparent. Workflows ensure that proposed changes are considered both from a medical and scientific perspective and from their value and place in a particular use case. As a result, the Foundation Component and the related tabular list(s) will be released in updated versions.

 

As with other ICD chapters, the TM1 chapter is not judging TM practice or the efficacy of any TM intervention. As a tool for classifying, diagnosing, counting, communicating and comparing TM conditions, it will also assist research and evaluation to assess the safety and efficacy of TM.

1.6.1 ICD–11 Update Process

Official releases of the ICD-11 MMS classification are produced annually for international use in mortality and morbidity (blue browser). A standardised process has been established to ensure that the proposed updates are collected, routed, reviewed, and duly considered before being implemented. The updating is carried out at different levels with different frequencies. Updates that impact on the 4 and 5 digit structures will be published every 5 years. Updates at a more detailed level can be published more frequently. Additions to the index can be done on an ongoing basis. Mortality and morbidity rules that have serious impact on statistics will be updated in long term cycles of 10 years.

1.6.1.1 Proposals and Review Mechanisms and workflow

Any individual can submit a proposal for an update to the ICD. Such updates can refer to one or more entities of the ICD. They may address the position of entities in a tabular list, in the Foundation Component, and any element of the content model. The maintenance platform of ICD-11 (orange browser) is used for proposals and comments. Any input to ICD-11 and its components requires proper mention of sources, scientific evidence, and permission by the owner of the copyright, where applicable.

1.6.2 Applicability and Intellectual Property

The following paragraph provides an overview of the legal regulations in relation to ICD. It is understood that this text does not prejudge in any way the wording of the legal arrangements that are made between WHO and the relevant parties.

The ICD is intellectual property of WHO and changes to the ICD are subject to contractual arrangements and approval through the updating mechanism.

ICD is distributed free of charge.

Users may access and use the ICD from the Internet for personal use. Users will register and agree to the end user license agreement prior to accessing ICD files for download.

Web services for ICD coding and browsing are available subject relevant agreements.

The ICD may be translated into any language. For translation, interested parties (the Translator) are requested to contact the WHO and comply with the relevant regulations in a contract. The Translator will use the WHO translation platform, thus allowing the WHO to verify correctness and completeness of the translation. The translations of WHO official languages are a product of WHO and all rights are vested with WHO. Translations of other languages are a product of the Translator. WHO is automatically granted a perpetual and irrevocable, non-exclusive, world-wide, royalty-free, sub-licensable right to use, change, adapt, translate, publish, and disseminate such work product in any manner and in any format in conjunction with the work of WHO. Any adaptation, translation, publication (including in scientific journals), and dissemination to be made by either party will be coordinated between them.

In some instances, users may feel the need to change parts of the ICD in order to produce a special version of ICD. Production of special versions require a dedicated contractual arrangement with WHO.
Such versions will be produced from the WHO production platform by WHO. All changes to ICD must be submitted on the WHO-ICD maintenance platform (for details see Section 1.6.1 ICD–11 Update Process).
Requests for production of a special version will be subject to requests for funding of the related work.

For international reporting, the most up to date version of the ICD is used, as stipulated in the Nomenclature Regulations (1967).

No publicity may be displayed in the coding or browsing pages. In case of embedding in a local website, or running a local version, a link to the ICD homepage at the WHO must be included. No publicity may be displayed in the ICD print versions.

Ideally users will access the ICD online or through the web services. This will ensure proper joint use of index, content model, and tabular lists and facilitate dissemination of updates, where applicable. Any coding mechanism produced by 3rd parties must provide the same coding results as the reference online coding tool.

1.6.3 National Modifications for morbidity coding

The use of ICD in the specific context of the health care system of a country may require the development of modifications to the ICD-11, for example, due to specific settings or due to reimbursement system requirements. Such changes will be subject to the same international process as are all other changes to ICD, then become part of the Foundation Component and eventually of the MMS, prior to their implementation in the requesting country.

A situation may arise, where a national government or an equally important national body needs a modification to be implemented immediately. In such circumstances, conflicts with the current Foundation Component must be avoided, and the relevant changes will be subject to special mechanisms of the international updating process. All countries planning to produce national modifications must make relevant contractual arrangements with WHO. This includes regulations on distribution within the respective country and the resources necessary.

For developing a national modification of ICD-11 the following rules must be followed:

1. Modifications will be ideally agreed by the ICD-11 maintenance bodies before they are implemented nationally
2. Modifications should not impact on Morbidity and Mortality Statistics, and should not conflict with the foundation.
3. National modifications will consider if suitable additional detail exists already in the foundation.
4. If a change is performed to the international version the respective national modification must be adapted as soon as possible.

Example

‘Diabetes Type 1’ in WHO Version of ICD-11 is 5A10. In a national modification there might be the need for additional detail which can be added in the routine notation of ICD-11 codes: ‘Diabetes Type 1, uncontrolled’ can be coded in that national modification to 5A10; Diabetes Type 1, uncontrolled’ to 5A10.1 However, the mechanisms for postcoordination via cluster coding would allow to code that detail without additional pre-coordination.

1.7 History of the development of the ICD

1.7.1 Early history

Sir George Knibbs, the eminent Australian statistician, credited François Bossier de Lacroix (1706-1777), better known as Sauvages, with the first attempt to classify diseases systematically (1). Sauvages’ comprehensive treatise was published under the title Nosologia methodica. A contemporary of Sauvages was the great methodologist Linnaeus (1707-1778), author of Genera morborum, a catalogue of diseases. More recently, Moriyama et al (2) have referred to 16th century and 17th predecessors Fernel and Sydenham. At the beginning of the 19th century, the classification of disease in most general use was one by William Cullen (1710- 1790, of Edinburgh, which was published in 1785 under the title Synopsis nosologiae methodicae.

For all practical purposes, however, the statistical study of disease began a century earlier with the work of John Graunt on the London Bills of Mortality published in 1662. The kind of classification envisaged by this pioneer is exemplified by his attempt to estimate the proportion of liveborn children who died before reaching the age of six, when no records of age at death were available. He took all deaths classed them using terms from the time, such as thrush, convulsions, rickets, teeth and worms, abortives, chrysomes, infants, livergrown, and overlaid and added to them half the deaths classed as smallpox, swinepox, measles, and worms without convulsions. Despite the crudity of this classification, his estimate of 36% mortality before the age of six years appears from later evidence to have been a good one. While three centuries have contributed to the scientific accuracy of disease classification, there are many who doubt the usefulness of attempts to compile statistics of disease, or even causes of death, because of the difficulties of classification. To these, one can quote Major Greenwood: ‘The scientific purist, who will wait for medical statistics until they are nosologically exact, is no wiser than Horace’s rustic waiting for the river to flow away’ (3).

Fortunately for the progress of preventive medicine, the General Register Office of England and Wales, at its inception in 1837, found in William Farr (1807-1883) – its first medical statistician. Farr was a man who not only made the best possible use of the imperfect classifications of disease available at the time, but laboured to secure better classifications and international uniformity in their use.

Farr found Cullen’s classification in use in the public services. It had not been revised to embody the advances of medical science, nor was it deemed by him to be satisfactory for statistical purposes. Farr realised that small numbers that would result from a detailed classification would not permit statistical inferences to be made. In the first Annual Report of the Registrar General (4), therefore, he discussed the principles that should govern a statistical classification of disease and urged the adoption of a uniform classification as follows:

The advantages of a uniform statistical nomenclature, however imperfect, are so obvious, that it is surprising no attention has been paid to its enforcement in Bills of Mortality. Each disease has, in many instances, been denoted by three or four terms, and each term has been applied to as many different diseases: vague, inconvenient names have been employed, or complications have been registered instead of primary diseases. The nomenclature is of as much importance in this department of inquiry as weights and measures in the physical sciences, and should be settled without delay.

Both nomenclature and statistical classification received constant study and consideration by Farr in his annual ‘Letters’ to the Registrar General published in the Annual Reports of the Registrar General. Farr did much to promote his classification but could not find general acceptance (4). The utility of a uniform classification of causes of death was so strongly recognized at the first International Statistical Congress, held in Brussels in 1853, that the Congress requested William Farr and Genevan Marc d’Espine to prepare an internationally applicable, uniform classification of causes of death.

At the next Congress, in Paris in 1855, Farr and d’Espine submitted two separate lists which were based on very different principles. Farr’s classification was arranged under five groups: epidemic diseases, constitutional (general) diseases, local diseases arranged according to anatomical site, developmental diseases, and diseases that are the direct result of violence. D’Espine classified diseases according to their nature (gouty, herpetic, haematic, etc.). The Congress adopted a compromise list of 139 rubrics. In 1864, this classification was revised in Paris on the basis of Farr’s model and was subsequently further revised in 1874, 1880, and 1886. Although this classification was never universally accepted, the general arrangement proposed by Farr, including the principle of classifying diseases by aetiology followed by anatomical site, survived as the basis of the International List of Causes of Death.

Importantly, the 1855 Congress also recommended that each country should ask for information on causes of death from the doctor who had been attending the deceased, and that each country should take measures to ensure that all deaths were verified by doctors (4).

1.7.2 Adoption of the International List of Causes of Death

At its 1891 meeting in Vienna, the International Statistical Institute, the successor to the International Statistical Congress, charged a committee chaired by Jacques Bertillon (1851- 1922), Chief of Statistical Services of the City of Paris, with the preparation of a classification of causes of death. The committee’s report was presented and adopted at the meeting of the International Statistical Institute in Chicago in 1893.

For main headings, Bertillon adopted the anatomical site rather than the nature of disease, according to Farr’s plan. Bertillon’s list included defined diseases most worthy of study by reason of their transmissible nature or their frequency of occurrence. In accordance with the instructions of the Vienna Congress, Bertillon included three classifications: an abridged classification of 44 titles; a classification of 99 titles; and a classification of 161 titles. Bertillon also prepared some rules or guidelines on the resolution of problems; for example, how statistical clerks should classify what is written without imputing what the doctor might have meant (5). The ‘Bertillon Classification of Causes of Death’, as it was first called, received general approval and was adopted by several countries, as well as by many cities. The classification was first used in North America by Jesus E. Monjaras for the statistics of San Luis de Potosi, Mexico (5). In 1898, the American Public Health Association, at its meeting in Ottawa, Canada, recommended the adoption of the Bertillon Classification by registrars of Canada, Mexico, and the United States of America. The Association further suggested that the classification should be revised every ten years.

At the meeting of the International Statistical Institute at Christiania in 1899, Bertillon presented a report on the progress of the classification, including the recommendations of the American Public Health Association for decennial revisions. The International Statistical Institute then adopted the following resolution (6): The International Statistical Institute, convinced of the necessity of using in the different countries comparable nomenclatures:

Learns with pleasure of the adoption by all the statistical offices of North America, by some of those of South America, and by some in Europe, of the system of cause of death nomenclature presented in 1893; Insists vigorously that this system of nomenclature be adopted in principle and without revision, by all the statistical institutions of Europe; Approves, at least in its general lines, the system of decennial revision proposed by the American Public Health Association at its Ottawa session (1898); Urges the statistical offices who have not yet adhered, to do so without delay, and to contribute to the comparability of the cause of death nomenclature.

The French Government therefore assembled in Paris, in August 1900, the first International Conference for the Revision of the Bertillon or International List of Causes of Death. Delegates from 26 countries attended this Conference. A detailed classification of causes of death consisting of 179 groups and an abridged classification of 35 groups was adopted on 21 August 1900. The desire for decennial revisions was recognized, and the French Government was requested to call the next meeting in 1910. In fact, the next conference was held in 1909, and the Government of France called succeeding conferences in 1920, 1929, and 1938. Bertillon continued to be the guiding force in the promotion of the International List of Causes of Death, and the revisions of 1900, 1910, and 1920 were carried out under his leadership. As Secretary- General of the International Conference, he sent out the provisional revision for 1920 to more than 500 people, asking for comments. His death in 1922 left the International Conference without a guiding hand.

At the 1923 session of the International Statistical Institute, Michel Huber, Bertillon’s successor in France, recognized this lack of leadership and introduced a resolution for the International Statistical Institute to renew its stand of 1893 in regard to the International Classification of Causes of Death and to cooperate with other international organisations in preparation for subsequent revisions. The Health organisation of the League of Nations had also taken an active interest in vital statistics and appointed a Commission of Statistical Experts to study the classification of diseases and causes of death, as well as other problems in the field of medical statistics. E. Roesle, Chief of the Medical Statistical Service of the German Health Bureau and a member of the Commission of Statistical Experts, prepared a monograph that listed the expansion in the rubrics of the 1920 International List of Causes of Death that would be required if the classification were to be used in the tabulation of statistics of morbidity. This careful study was published by the Health organisation of the League of Nations in 1928 (7). In order to coordinate the work of both agencies, an international ‘Mixed Commission’ was created with an equal number of representatives from the International Statistical Institute and the Health organisation of the League of Nations. This Commission drafted the proposals for the Fourth (1929) and the Fifth (1938) revisions of the International List of Causes of Death.

1.7.3 The Fifth Decennial Revision Conference

The Fifth International Conference for the Revision of the International List of Causes of Death, like the preceding conferences, was convened by the Government of France and was held in Paris in October 1938. The Conference approved three lists: a detailed list of 200 titles, an intermediate list of 87 titles and an abridged list of 44 titles. Apart from bringing the lists up to date in accordance with the progress of science, particularly in the chapter on infectious and parasitic diseases, and changes in the chapters on puerperal conditions and on accidents, the Conference made as few changes as possible in the contents, number, and even in the numbering of the items. A list of causes of stillbirth was also drawn up and approved by the Conference.

As regards classification of diseases for morbidity statistics, the Conference recognized the growing need for a corresponding list of diseases to meet the statistical requirements of widely differing organisations, such as health insurance organisations, hospitals, military medical services, health administrations, and similar bodies. The following resolution, therefore, was adopted (8):

1.7.3.1 International Lists of Diseases

·         In view of the importance of the compilation of international lists of diseases corresponding to the international lists of causes of death: The Conference recommends that the Joint Committee appointed by the International Institute of Statistics and the Health organisation of the League of Nations undertake, as in 1929, the preparation of international lists of diseases, in conjunction with experts and representatives of the organisations specially concerned. Pending the compilation of international lists of diseases, the Conference recommends that the various national lists in use should, as far as possible, be brought into line with the detailed International List of Causes of Death (the numbers of the chapters, headings and subheadings in the said List being given in brackets). The Conference further recommended that the United States Government continue its studies of the statistical treatment of joint causes of death in the following resolution (9):

o    Death Certificate and Selection of Causes of Death where more than One Cause is given (Joint Causes) The Conference,

• Whereas, in 1929, the United States Government was good enough to undertake the study of the means of unifying the methods of selection of the main cause of death to be tabulated in those cases where two or more causes are mentioned on the death certificate,
• And whereas, the numerous surveys completed or in the course of preparation in several countries reveal the importance of this problem, which has not yet been solved,
• And whereas, according to these surveys, the international comparability of death rates from the various diseases requires, not only the solution of the problem of the selection of the main tabulated cause of death, but also the solution of a number of other questions;

o    Warmly thanks the United States Government for the work it has accomplished or promoted in this connection;

·         Requests the United States Government to continue its investigations during the next ten years, in cooperation with other countries and organisations, on a slightly wider basis, and

·         Suggests that, for these future investigations, the United States Government should set up a subcommittee comprising representatives of countries and organisations participating in the investigations undertaken in this connection.

1.7.4 Previous classifications of diseases for morbidity statistics

In the discussion so far, classification of disease has been presented almost wholly in relation to cause-of-death statistics. Farr, however, recognized that it was desirable “to extend the same system of nomenclature to diseases which, though not fatal, cause disability in the population, and now figure in the tables of the diseases of armies, navies, hospitals, prisons, lunatic asylums, public institutions of every kind, and sickness societies, as well as in the census of countries like Ireland, where the diseases of all the people are enumerated” (10). In his ‘Report on nomenclature and statistical classification of diseases’, presented to the Second International Statistical Congress, he therefore included in the general list of diseases most of those diseases that affect health as well as diseases that are fatal. At the Fourth International Statistical Congress, held in London in 1860, Florence Nightingale urged the adoption of Farr’s classification of diseases for the tabulation of hospital morbidity in the paper, ‘Proposals for a uniform plan of hospital statistics’.

At the First International Conference to revise the Bertillon Classification of Causes of Death in Paris in 1900, a parallel classification of diseases for use in statistics of sickness was adopted. A parallel list was also adopted at the second conference in 1909. The extra categories for non-fatal diseases were formed by subdivision of certain rubrics of the cause-of-death classification into two or three disease groups, each of these being designated by a letter. The translation in English of the Second Decennial Revision, published by the United States Department of Commerce and Labor in 1910, was entitled International Classification of Causes of Sickness and Death. Later revisions incorporated some of the groups into the detailed International List of Causes of Death. The Fourth International Conference adopted a classification of illness which differed from the detailed International List of Causes of Death only by the addition of further subdivisions of 12 titles. These international classifications of illnesses, however, failed to receive general acceptance, as they provided only a limited expansion of the basic cause-of-death list.

In the absence of a uniform classification of diseases that could be used satisfactorily for statistics of illness, many countries found it necessary to prepare their own lists. A Standard Morbidity Code was prepared by the Dominion Council of Health of Canada and published in 1936. The main subdivisions of this code represented the 18 chapters of the 1929 Revision of the International List of Causes of Death, and these were subdivided into some 380 specific disease categories. At the Fifth International Conference in 1938, the Canadian delegate introduced a modification of this list for consideration as the basis for an international list of causes of illness. Although no action was taken on this proposal, the Conference adopted the resolution quoted above.

In 1944, provisional classifications of diseases and injuries were published in both the United Kingdom and the United States for use in the tabulation of morbidity statistics. Both classifications were more extensive than the Canadian list, but, like it, followed the general order of diseases in the International List of Causes of Death. The British classification was prepared by the Committee on Hospital Morbidity Statistics of the Medical Research Council, which was created in January 1942. It is entitled ‘A provisional classification of diseases and injuries for use in compiling morbidity statistics’ (8). It was prepared with the purpose of providing a scheme for collecting and recording statistics of patients admitted to hospitals in the United Kingdom, using a standard classification of diseases and injuries, and was used throughout the country by governmental and other agencies.

A few years earlier, in August 1940, the Surgeon-General of the United States Public Health Service and the Director of the United States Bureau of the Census published a list of diseases and injuries for tabulation of morbidity statistics (9). The code was prepared by the Division of Public Health Methods of the Public Health Service in cooperation with a committee of consultants appointed by the Surgeon-General. ‘The Manual for coding causes of illness according to a diagnosis code for tabulating morbidity statistics’, consisting of the diagnosis code, a tabular list of inclusions, and an alphabetical index, was published in 1944. The code was used in several hospitals, in a large number of voluntary hospital insurance plans and medical care plans, and in special studies by other agencies in the United States.

1.7.5 United States Committee on Joint Causes of Death

In compliance with the resolution of the Fifth International Conference, the American Secretary of State in 1945 appointed the United States Committee on Joint Causes of Death under the chairmanship of Lowell J. Reed, Professor of Biostatistics at Johns Hopkins University. Members and consultants of this committee included representatives of the Governments of Canada and the United Kingdom and the Health Section of the League of Nations. Recognizing a trend, the committee decided that it would be advantageous to consider classifications from the point of view of morbidity and mortality, since the problem of joint causes pertained to both types of statistics.

The committee also took into account that part of the resolution on International Lists of Diseases of the previous International Conference recommending that the ‘various national lists in use should, as far as possible, be brought into line with the detailed International List of Causes of Death’. It recognized that the classification of sickness and injury is closely linked with the classification of causes of death. The view that such lists are fundamentally different arises from the erroneous belief that the International List is a classification of terminal causes, whereas it is in fact based upon the morbid condition that initiated the train of events ultimately resulting in death. The committee believed that, in order to utilize fully both morbidity and mortality statistics, not only should the classification of diseases for both purposes be comparable, but if possible there should be a single list.

Furthermore, an increasing number of statistical organisations were using medical records involving both sickness and death. Even in organisations that compile only morbidity statistics, fatal as well as non-fatal cases needed to be coded. A single list, therefore, greatly facilitates their coding operations. It also provides a common base for comparison of morbidity and mortality statistics.

A subcommittee was therefore appointed, which prepared a draft of a Proposed Statistical Classification of Diseases, Injuries and Causes of Death. A final draft was adopted by the committee after it had been modified on the basis of trials undertaken by various agencies in Canada, the United Kingdom and the United States of America.

1.7.6 Sixth Revision of the International Lists

The International Health Conference held in New York City in June and July 1946 (11) entrusted the Interim Commission of the World Health Organisation with the responsibility of:

reviewing the existing machinery and of undertaking such preparatory work as may be necessary in connection with: (i) the next decennial revision of ‘The International Lists of Causes of Death’ (including the lists adopted under the International Agreement of 1934, relating to Statistics of Causes of Death); and (ii) the establishment of International Lists of Causes of Morbidity

To meet this responsibility, the Interim Commission appointed the Expert Committee for the Preparation of the Sixth Decennial Revision of the International Lists of Diseases and Causes of Death. This Committee, taking full account of prevailing opinion concerning morbidity and mortality classification, reviewed and revised the above mentioned proposed classification which had been prepared by the United States Committee on Joint Causes of Death.

The resulting classification was circulated to national governments preparing morbidity and mortality statistics for comments and suggestions under the title, International Classification of Diseases, Injuries, and Causes of Death. The Expert Committee considered the replies and prepared a revised version incorporating changes to improve the utility and acceptability of the classification. The Committee also compiled a list of diagnostic terms to appear under each title of the classification. Furthermore, a subcommittee was appointed to prepare a comprehensive alphabetical index of diagnostic statements classified to the appropriate category of the classification. The Committee also considered the structure and uses of special lists of causes for tabulation and publication of morbidity and mortality statistics and studied other problems related to the international comparability of mortality statistics, such as form of medical certificate and rules for classification. The International Conference for the Sixth Revision of the International Lists of Diseases and Causes of Death was convened in Paris from 26 to 30 April 1948 by the Government of France under the terms of the agreement signed at the close of the Fifth Revision Conference in 1938. Its secretariat was entrusted jointly to the competent French authorities and to the World Health Organisation, which had carried out the preparatory work under the terms of the arrangement concluded by the governments represented at the International Health Conference in 1946 (12).

The Conference adopted the classification prepared by the Expert Committee as the Sixth Revision of the International Lists (13). It also considered other proposals of the Expert Committee concerning the compilation, tabulation and publication of morbidity and mortality statistics. The Conference approved the International Form of Medical Certificate of Cause of Death, accepted the underlying cause of death as the main cause to be tabulated, and endorsed the rules for selecting the underlying cause of death as well as the special lists for tabulation of morbidity and mortality data. It further recommended that the World Health Assembly should adopt regulations under Article 21(b) of the WHO Constitution to guide Member States in compiling morbidity and mortality statistics in accordance with the International Statistical Classification. In 1948, the First World Health Assembly endorsed the report of the Sixth Revision Conference and adopted World Health Organisation Regulations No. 1, prepared on the basis of the recommendations of the Conference. The International Classification, including the Tabular List of Inclusions defining the content of the categories, was incorporated, together with the form of the medical certificate of cause of death, the rules for classification and the special lists for tabulation, into the Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Death (22). The Manual consisted of two volumes, Volume 2 being an alphabetical index of diagnostic terms coded to the appropriate categories. In the Sixth Revision, morbid conditions resulting from injuries, poisonings and other external causes were classified according to both the external circumstances giving rise to the injury and to the kind of injury.

The adoption of this dual classification was regarded at the time as a bold step to deal with the simultaneous interest in more than one aspect of injury. The Sixth Decennial Revision Conference marked the beginning of a new era in international vital and health statistics. Apart from approving a comprehensive list for both mortality and morbidity and agreeing on international rules for selecting the underlying cause of death, it recommended the adoption of a comprehensive programme of international cooperation in the field of vital and health statistics. An important item in this programme was the recommendation that governments establish national committees on vital and health statistics to coordinate the statistical activities in the country, and to serve as a link between the national statistical institutions and the World Health Organisation. It was further envisaged that such national committees would, either singly or in cooperation with other national committees, study statistical problems of public health importance and make the results of their investigations available to the WHO.

1.7.7 The Seventh and Eighth Revisions

The International Conference for the Seventh Revision of the International Classification of Diseases was held in Paris under the auspices of the WHO in February 1955 (14). In accordance with a recommendation of the WHO Expert Committee on Health Statistics, this revision was limited to essential changes and amendments of errors and inconsistencies (15). The Eighth Revision Conference convened by the WHO met in Geneva, from 6 to 12 July 1965 (16). This revision was more radical than the Seventh but left unchanged the basic structure of the Classification and the general philosophy of classifying diseases, whenever possible, according to their aetiology rather than a particular manifestation. During the years that the Seventh and Eighth Revisions of the ICD were in force, the use of the ICD for indexing hospital medical records increased rapidly and some countries prepared national adaptations which provided the additional detail needed for this application of the ICD.

1.7.8 The Ninth Revision

The International Conference for the Ninth Revision of the International Classification of Diseases, convened by the WHO, met in Geneva from 30 September to 6 October 1975 (17). In the discussions leading up to the conference, it had originally been intended that there should be little change other than updating of the classification. This was mainly because of the expense of adapting data processing systems each time the classification was revised. There had been an enormous growth of interest in the ICD and ways had to be found of responding to this, partly by modifying the classification itself and partly by introducing special coding provisions.

A number of representations were made by specialist bodies which had become interested in using the ICD for their own statistics. Some subject areas in the classification were regarded as inappropriately arranged and there was considerable pressure for more detail and for adaptation of the classification to make it more relevant for the evaluation of medical care, by classifying conditions to the chapters concerned with the part of the body affected rather than to those dealing with the underlying generalised disease. At the other end of the scale, there were representations from countries and areas where a detailed and sophisticated classification was irrelevant, but which nevertheless needed a classification based on the ICD in order to assess their progress in health care and in the control of disease. The final proposals presented to and accepted by the Conference retained the basic structure of the ICD, although with much additional detail at the level of the four-digit subcategories, and some optional five-digit subdivisions. For the benefit of users not requiring such detail, care was taken to ensure that the categories at the three-digit level were appropriate.

For the benefit of users wishing to produce statistics and indexes oriented towards medical care, the Ninth Revision included an optional alternative method of classifying diagnostic statements, including information about both an underlying general disease and a manifestation in a particular organ or site. This system became known as the dagger and asterisk system. The Twenty Ninth World Health Assembly, noting the recommendations of the International Conference for the Ninth Revision of the International Classification of Diseases, approved the publication, for trial purposes, of supplementary classifications of Impairments and Handicaps and of Procedures in Medicine as supplements to, but not as integral parts of, the International Classification of Diseases.

1.7.9 The Tenth Revision

Even before the Conference for the Ninth Revision, the WHO had been preparing for the Tenth Revision. It recognised that the great expansion in the use of the ICD necessitated a thorough rethinking of its structure and an effort to devise a stable and flexible classification, which should not require fundamental revision for many years to come. The WHO Collaborating Centres for Classification of Diseases (see www.who.int/classification) were consequently called upon to experiment with models of alternative structures for ICD–10.

It had also become clear that the established ten-year interval between revisions was too short. Work on the revision process had to start before the current version of the ICD had been in use long enough to be thoroughly evaluated, mainly because the necessity to consult so many countries and organisations made the process a very lengthy one. The Director General of the WHO therefore wrote to the Member States and obtained their agreement to postpone a 1985 Tenth Revision Conference until 1989, and to delay the introduction of the Tenth Revision which would have been due in 1989. In addition to permitting experimentation with alternative models for the structure of the ICD, this allowed time for the evaluation of ICD 9, for example through meetings organised by some of the WHO Regional Offices and through a survey organised at headquarters.

The International Conference for the Tenth Revision of the International Classification of Diseases, attended by delegates from 43 Member States, was convened by the World Health organisation in Geneva from 26 September to 2 October 1989. The United Nations, the International Labour Organisation, and the WHO Regional Offices sent representatives to participate in the Conference, as did the Council for International organisations of Medical Sciences. Twelve other non-governmental organisations concerned with cancer registration, the deaf, epidemiology, family medicine, gynaecology and obstetrics, hypertension, health records, preventive and social medicine, neurology, psychiatry, rehabilitation and sexually transmitted diseases were also invited.

Extensive preparatory activity had been devoted to a radical review of the suitability of the structure of the ICD, essentially a statistical classification of diseases and other health problems, to serve a wide variety of needs for mortality and health-care data. Ways of stabilizing the coding system to minimize disruption at successive revisions had been investigated, as had the possibility of providing a better balance between the content of the different chapters of the ICD. Even with a new structure, it was plain that one classification could not cope with the extremes of the requirements. The concept had therefore been developed of a ‘family’ of classifications, which would include the ICD for traditional mortality and morbidity statistics, while needs for more detailed, less detailed or different classifications and associated matters would be dealt with by other members of the family. The potential for different members of the ‘family’ in the medico-social and multi-dimensional assessment in relation not only to health but also to activities of daily living, as well as the social and physical environment, was recognised. It was demonstrated that effective information could be obtained through use of the ICD and the International Classification of Impairments, Disabilities, and Handicaps (ICIDH) (18), and through use of the codes from Chapter XXI of the Tenth Revision.

The main innovation in the Tenth Revision was the use of an alphanumeric coding scheme of one letter followed by three numbers at the four-character level. This had the effect of more than doubling the size of the coding frame in comparison with the Ninth Revision and enabled the vast majority of chapters to be assigned a unique letter or group of letters, each capable of providing 100 three-character categories. Of the 26 available letters, 25 had been used, the letter U being left vacant for future additions and changes, and for possible interim classifications to solve difficulties arising at the national and international level between revisions.

Another important innovation was the creation towards the end of certain chapters of categories for postprocedural disorders. These identified important conditions that constituted a medical care problem in their own right. Postprocedural conditions that were not specific to a particular body system continued to be classified in the chapter on ‘Injury, poisoning and certain other consequences of external causes’. The Revision included definitions, standards, and reporting requirements related to maternal mortality and to foetal, perinatal, neonatal and infant mortality. It was published in three volumes: one containing the Tabular List, a second containing all related definitions, standards, rules and instructions, and a third containing the Alphabetical Index.

The Tenth Revision Conference discussed the difficulties experienced during the extended period of use of the Ninth Revision, related to the emergence of new diseases and the lack of an updating mechanism to accommodate them. It recognized that it would not be feasible to hold revision conferences more frequently than every 10 years. It also recognized that any changes introduced during the lifetime of the Tenth Revision would need to be considered carefully in relation to their impact on analyses and trends.

1.7.10 The WHO Family of International Classifications

Although the ICD is suitable for many different applications, it does not serve all the needs of its various users. It does not provide sufficient detail for some specialties and sometimes information on different attributes of health conditions may be needed. Also, the ICD is not useful to describe functioning and disability as aspects of health and does not include a full array of health interventions or reasons for encounter. Foundations laid by the International Conference on ICD–10 in 1989 provided the basis for the development of a ‘family’ of health classifications. This was given added momentum during the 1990s by the development of the International Classification of Functioning, Disability and Health (ICF) (19), approved by the World Health Assembly in 2001.

In 2001, the WHO Family of International Classifications (WHO-FIC) was created. At the core of the Family are its reference classifications, currently the ICD and the ICF; the International Classification of Health Interventions (ICHI), now under development, is the third reference classification. The WHO-FIC also includes derived classifications, which provide additional detail to core classifications or are rearrangements or aggregations of terms in core classifications; the WHO has licensed several countries to develop national modifications of the ICD as derived classifications. As well, the WHO-FIC includes related classifications to cover health functions which are not (or are only partially) covered by other WHO-FIC members. The WHO-FIC is supported by a network of Collaborating Centres, based on the former Collaborating Centres for the ICD and the ICF, but continuously expanded by the addition of new centres.

Table 1: Evolution of ICD

Iteration	Year	Document	Note
0	1891	Bertillon Classification of Causes of Death	Drafted by International Statistical Institute
1	1900	Bertillon/International List of Causes of Death	First International Conference for Revision of List of Causes of Death
2	1910	International List of Causes of Death	179 titles, call for revision every 10 years
3	1920	International List of Causes of Death
4	1929	International List of Causes of Death	Drafted jointly by International Statistical Institute and Health organisation of the League of Nations
5	1938	International List of Causes of Death	200 titles, additions to infectious and parasitic
6	1948	International Classification of Diseases, Injuries, and Causes of Death	Recognition of classification of disease and injury, in addition to causes of death
7	1955	International Classification of Diseases, Injuries, and Causes of Death
8	1965	International Classification of Diseases, Injuries, and Causes of Death
9	1975	International Classification of Diseases, Injuries, and Causes of Death	Trial of supplement on Impairments and Handicaps, and Procedures in Medicine
10	1989	International Statistical Classification of Diseases and Related Health Problems	Introduction of alpha-numeric coding scheme, postprocedural disorders; regular interim updates
11	2018	International Statistical Classification of Diseases and Related Health Problems	Postcoordination (cluster coding); addition of Traditional Medicine, adverse events coding

1.7.11 Updating of ICD between revisions

As foreshadowed at the Tenth Revision conference, updating of the tenth revision of ICD commenced in 2000. Updating proposals came from, and were carefully considered by, the WHO and Collaborating Centres, including the impact on trends. The updating process has allowed an extended life for the Tenth Revision while maintaining its clinical and scientific currency.

1.7.12 Preparations for the Eleventh Revision

By 2003, it was becoming clear to the WHO and the Collaborating Centres that a further revision of the ICD could not be long delayed. The extent to which ICD updating could encapsulate emerging developments was limited by the structure of ICD–10, and some issues needed extended development and discussion with expert groups. A special meeting of Collaborating Centres in Helsinki in 2004 discussed the need for a revision and issues to be addressed as part of the revision process. The 2004 WHO-FIC meeting subsequently adopted a revision process work-plan which was progressively developed at ensuing meetings.

In 2007, the WHO formally launched the revision process. Oversight has been provided through a broad-based Revision Steering Group. Technical work has been undertaken by a series of Topic Advisory Groups, with cross-cutting groups examining mortality, morbidity and quality and safety issues. For the first time, a chapter on description of diseases and patterns of diseases from a Traditional medicine standpoint has been included.

A Content Model, including a range of components for each ICD entity has been developed, giving a rich Foundation for the ICD. Other classifications and terminologies are linked or included where possible to ensure ICD is aligned with them, and items used in other members of the WHO Family of Classifications have been aligned wherever possible. The more traditional statistical classification for mortality and morbidity is obtained from the Foundation Component of ICD–11 as a tabular list. Extension codes are used to limit content volume but still allow detailed classification of disease entities. Supplementary chapters and sections allow capturing on an optional basis information about traditional medicine diagnoses and functioning. Based on the experiences with ICD-9 and ICD-10 and updating mechanisnm was designed, that allows improvements in user guidance and scientific updates without compromising the statistical use of the classification.

1.7.13 References for history of ICD

1. Knibbs G.H. The International Classification of Disease and Causes of Death and its revision. Medical journal of Australia, 1929, 1:2-12.
2. Moriyama IM, Loy RM, Robb-Smith AHT. History of the statistical classification of diseases and causes of death. Rosenberg HM, Hoyert DL, eds. Hyattsville, MD: National Center for Health Statistics. 2011.
3. Greenwood M. Medical statistics from Graunt to Farr. Cambridge, Cambridge University Press, 1948.
4. First annual report. London, Registrar General of England and Wales, 1839, p. 99.
5. Bertillon J. Classification of the causes of death (abstract). In: Transactions of the 15th International Congress on Hygiene Demography. Washington, 1912.
6. International list of causes of death. The Hague, International Statistical Institute, 1940.
7. Roesle E. Essai d’une statistique comparative de la morbidité devant servir à établir les listes spéciales des causes de morbidité. Geneva, League of Nations Health organisation, 1928 (document C.H. 730)
8. Medical Research Council, Committee on Hospital Morbidity Statistics. A provisional classification of diseases and injuries for use in compiling morbidity statistics. London, Her Majesty’s Stationery Office, 1944 (Special Report Series No. 248).
9. US Public Health Service, Division of Public Health Methods. Manual for coding causes of illness according to a diagnosis code for tabulating morbidity statistics. Washington, Government Publishing Office, 1944 (Miscellaneous Publication No. 32).
10. Sixteenth annual report. London, Registrar General of England and Wales, 1856, App. p.73.
11. Official Records of the World Health Organisation, 1948, 11, 23.
12. Official Records of the World Health Organisation, 1948, 2, 110.
13. Manual of the international statistical classification of diseases, injuries, and causes of death. Sixth revision. Geneva, World Health Organisation, 1949.
14. Report of the International Conference for the Seventh Revision of the International Lists of Diseases and Causes of Death. Geneva, World Health Organisation, 1955 (unpublished document WHO/HA/7 Rev. Conf./17 Rev. 1.
15. Third Report of the Expert Committee on Health Statistics. Geneva, World Health organisation, 1952 (WHO Technical Report Series, No. 53).
16. Report of the International Conference for the Eighth Revision of the International Classification of Diseases. Geneva, World Health Organisation, 1965 (unpublished document WHO/ICD9/74.4.
17. Manual of the international statistical classification of diseases, injuries, and causes of death, Volume 1. Geneva, World Health Organisation, 1977.
18. International Classification of Impairments, Disabilities, and Handicaps. Geneva, World Health Organisation, 1980.
19. International Classification of Functioning, Disability and Health. Geneva, World Health organisation, 2001

 

Reference: https://icd.who.int/icd11refguide/en/index.html?r#1.1.0Part1purposeandmultipleusesofICD|part-1-an-introduction-to-icd11|c1

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