International Classification of Diseases (ICD)

The International Classification of Diseases (ICD) is the product of decades of effort by hundreds of international experts in all aspects of mental health.

Their dedication and hard work have yielded an authoritative volume that defines and classifies mental disorders in order to improve diagnoses, treatment, and research.

Family of International Classifications

• International Classification of Diseases (ICD):
  • The ICD is the standard diagnostic tool for epidemiology, health management, and clinical purposes.
  • This includes the analysis of the general health situation of population groups.
  • It is used to monitor the incidence and prevalence of diseases and other health problems, providing a picture of the general health situation of countries and populations.
• International Classification of Functioning, Disability and Health (ICF):
  • The ICF is a classification of health and health-related domains.
  • As the functioning and disability of an individual occurs in a context, ICF also includes a list of environmental factors.
• International Classification of Health Interventions (ICHI):
  • Provides Member States, health care service providers and organisers, and researchers with a common tool for reporting and analysing the distribution and evolution of health interventions for statistical purposes.
  • It is structured with various degrees of specificity for use at the different levels of the health systems, and will use a commonly accepted terminology in order to permit comparison of data between countries and services.
• Other Classifications:
  • Derived classifications are based on the reference classifications (i.e. ICD and ICF).
  • Derived classifications may be prepared either by building on the reference classification structure and categories to provide additional detail beyond that provided by the reference classification, or they may be prepared through rearrangement or aggregation of items from one or more reference classifications.

What is the ICD?

ICD is the foundation for the identification of health trends and statistics globally, and the international standard for reporting diseases and health conditions. It is the diagnostic classification standard for all clinical and research purposes.

ICD defines the universe of diseases, disorders, injuries and other related health conditions, listed in a comprehensive, hierarchical fashion that allows for:

• Easy storage, retrieval and analysis of health information for evidenced-based decision-making;
• Sharing and comparing health information between hospitals, regions, settings and countries;
• Data comparisons in the same location across different time periods;
• Monitoring of the incidence and prevalence of diseases;
• Observing reimbursements and resource allocation trends;
• Keeping track of safety and quality guidelines;
• The counting of deaths as well as diseases;
• Injuries;
• Symptoms;
• Reasons for encounter;
• Factors that influence health status; and
• External causes of disease.

History of ICD

In 1860, during the international statistical congress held in London, Florence Nightingale made a proposal that was to result in the development of the first model of systematic collection of hospital data.

In 1893, a French physician, Jacques Bertillon, introduced the Bertillon Classification of Causes of Death at a congress of the International Statistical Institute in Chicago. It was the first international classification edition, and also known as the International List of Causes of Death.

A number of countries adopted Bertillon’s system, which was based on the principle of distinguishing between general diseases and those localised to a particular organ or anatomical site, as used by the City of Paris for classifying deaths.

Subsequent revisions represented a synthesis of English, German, and Swiss classifications, expanding from the original 44 titles to 161 titles. In 1898, the American Public Health Association (APHA) recommended that the registrars of Canada, Mexico, and the United States also adopt it.

The APHA also recommended revising the system every 10 years to ensure the system remained current with medical practice advances. As a result, the first international conference to revise the International Classification of Causes of Death took place in 1900, with revisions occurring every ten years thereafter.

At that time, the classification system was contained in one book, which included an Alphabetic Index as well as a Tabular List. The book was small compared with current coding texts. The revisions that followed contained minor changes, until the sixth revision of the classification system.

With the sixth revision, the classification system expanded to two volumes. The sixth revision included morbidity and mortality conditions, and its title was modified to reflect the changes: International Statistical Classification of Diseases, Injuries and Causes of Death (ICD).

Prior to the sixth revision, responsibility for ICD revisions fell to the Mixed Commission, a group composed of representatives from the International Statistical Institute and the Health Organisation of the League of Nations. In 1948, the World Health Organisation (WHO) assumed responsibility for preparing and publishing the revisions to the ICD every ten years. WHO sponsored the seventh and eighth revisions in 1957 and 1968, respectively. It later became clear that the established ten year interval between revisions was too short.

The WHO Nomenclature Regulations, adopted in 1967, stipulated that Member States use the most current ICD revision for mortality and morbidity statistics. The ICD has been revised and published in a series of editions to reflect advances in health and medical science over time.

ICD-10 was endorsed in May 1990 by the Forty-third World Health Assembly. It is cited in more than 20,000 scientific articles and used by more than 100 countries around the world.

A version of ICD-11 was released on 18 June 2018 to allow Member States to prepare for implementation, including translating ICD into their national languages. ICD-11 will be submitted to the 144th Executive Board Meeting in January 2019 and the Seventy-second World Health Assembly in May 2019 and, following endorsement, Member States will start reporting using ICD-11 on 1 January 2022.

The ICD is currently the most widely used statistical classification system for diseases in the world. In addition, some countries – including Australia, Canada, and the United States – have developed their own adaptations of ICD, with more procedure codes for classification of operative or diagnostic procedures.

A detailed history of the development of the ICD can be found here:

Iterations of ICD

• International List of Causes of Death: Adopted in 1893.
• ICD-1:
  • Published in 1900.
• ICD-2:
  • Published in 1910.
• ICD-3:
  • Published in 1921.
• ICD-4:
  • Published in 1930.
• ICD-5:
  • Published in 1939.
• ICD-6
  • Published in 1949.
  • The sixth revision included morbidity and mortality conditions, and its title was modified to reflect the changes: International Statistical Classification of Diseases, Injuries and Causes of Death (ICD).
  • Expanded to two volumes.
  • Included, for the first time, a section for mental disorders.
  • ICD-6 was heavily influenced by the Veterans Administration classification and included:
    • 10 categories for psychoses and psychoneuroses; and
    • 7 categories for disorders of character, behaviour, and intelligence.
• ICD-7:
  • Published in 1957.
• ICD-8:
  • Approved in 1966 and published in 1968.
  • ICD Adapted (ICDA) developed for use in the US, with ICDA-8a being published in 1968.
• ICD-9:
  • Published in 1975 and implemented in 1978, as two volumes.
  • ICD Clinical Modification (ICD-9-CM) was an adaption developed by the US National Centre for Health Statistics (NCHS), is updated annually on 01 October, and provides additional morbidity detail.
• ICD-10:
  • Published in 1992 as three volumes.
  • ICD-10-CM (for diagnosis codes) and ICD-10-PCS (for procedure codes) adopted for US.
  • ICD-10-CA is a clinical modification developed by the Canadian Institute for Health Information.
• ICD-11:
  • Published on 18 June 2018 and implemented on 01 January 2022.

International Classification of Procedures in Medicine (ICPM)

When ICD-9 was published by the WHO, the ICPM was also developed (1975) and published (1978).

The ICPM surgical procedures fascicle was originally created by the United States, based on its adaptations of ICD (called ICDA), which had contained a procedure classification since 1962.

ICPM is published separately from the ICD disease classification as a series of supplementary documents called fascicles (bundles or groups of items).

Each fascicle contains a classification of modes of laboratory, radiology, surgery, therapy, and other diagnostic procedures.

Many countries have adapted and translated the ICPM in parts or as a whole and are using it with amendments since then.

Further Information

Further information about ICD can be found at the World Health Organisation’s website here.