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The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease. Every health condition can be assigned to a unique category and given a code, up to six characters long. Such categories can include a set of similar diseases.

The International Classification of Diseases is published by the World Health Organization and used worldwide for morbidity and mortality statistics, reimbursement systems and automated decision support in medicine. This system is designed to promote international comparability in the collection, processing, classification, and presentation of these statistics. The ICD is a core classification of the WHO Family of International Classifications (WHO-FIC).

The ICD is revised periodically and is currently in its tenth edition. The ICD-10, as it is therefore known, was developed in 1992 to track mortality statistics. ICD-11 is planned for 2015 and will be revised using Web 2.0 principles. Annual minor updates and three-yearly major updates are published by the WHO. The ICD is part of a "family" of guides that can be used to complement each other, including also the International Classification of Functioning, Disability and Health which focuses on the domains of functioning (disability) associated with health conditions, from both medical and social perspectives.

In 1893, a French physician, Jacques Bertillon, introduced the Bertillon Classification of Causes of Death at the International Statistical Institute in Chicago. A number of countries adopted Dr. Bertillon’s system, and 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 ten 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 convened 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: Manual of 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 Organization of the League of Nations. In 1948, the World Health Organization (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.

In 1959, the U.S. Public Health Service published The International Classification of Diseases, Adapted for Indexing of Hospital Records and Operation Classification (ICDA). It was completed in 1962 and a revision of this adaptation – considered to be the seventh revision of ICD – expanded a number of areas to more completely meet the indexing needs of hospitals. The U.S. Public Health Service later published the Eighth Revision, International Classification of Diseases, Adapted for Use in the United States. Commonly referred to as ICDA-8, this classification system fulfilled its purpose to code diagnostic and operative procedural data for official morbidity and mortality statistics in the United States.

Historical synopsis

From the publication entitled Medical Classification in Canada: Past, Present and Future (April 1995)

The International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10) which was adopted by the World Health Assembly in 1990 is the most recent revision of an international classification which has its roots in the last century.


The first International List of Causes of Death (at that time called the Bertillon Classification of Causes of Death) was adopted by the International Statistical Institute at a meeting in Chicago


At a meeting of the American Public Health Association in Ottawa, the International List of Causes of Death (Bertillon Classification) was recommended for use by registrars of Canada, Mexico, and the United States of America.


The Government of France convened the first International Conference for the Revision of the Bertillon or International List of Causes of Death in 1900. The desirability of decennial revisions was recognized and the Government of France called the succeeding conferences in 1910, 1920, 1929, and 1938. Following the death of Jacques Bertillon in 1922, an international commission, known as the “Mixed Commission” was created with equal representation from the International Statistical Institute and the Health Organization of the League of Nations. This Commission drafted the proposals for the Fourth and Fifth revisions of the International List of Causes of Death.


The need for a parallel classification of diseases that affect health as well as diseases that are fatal was recognized even before the first International Conference for the Revision of the International List of Causes of Death. A number of subdivisions or expansions of the International List were produced over the years but failed to receive general acceptance. A number of countries produced national lists in the intervening years, including the Standard Morbidity Code for Canada, accepted by the Dominion Council for Health in 1938. A draft of the Canadian code was the only morbidity code presented at the Fifth International Conference for the Revision of the International List of Causes of Death. Recognizing the growing need for a corresponding international list of diseases, the 1938 Conference adopted a resolution that included a recommendation that various national lists “should, as far as possible, be brought into line with the detailed International List of Causes of Death”. There was a belief 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. Work by some members of a committee with representation from the United States, Canada, the United Kingdom, and the Health Section of the League of Nations produced a preliminary draft of a “Proposed Statistical Classification of Diseases, Injuries and Causes of Death”.


The International Conference for the Sixth Revision of the International Lists of Diseases and Causes of Death was convened in Paris. Later in the same year, the First World Health Assembly endorsed the report of the Revision Conference and the publication of the Manual of the International Statistical Classification of Diseases, Injuries, and Causes of Death (more commonly referred to as ICD-6).


Succeeding decennial revision conferences (in 1955, 1965 and 1975) recognized the increasing use of ICD for the indexing of hospital medical records. As a result, non fatal diseases, symptoms, and other conditions necessitating contact with health services became more prominent in the classification structure in the Seventh, Eighth and Ninth revisions. Other classification needs were also being recognized, beyond the scope of the ICD. Based on the recommendations of the International Conference for the Ninth Revision (1975), the World Health Assembly approved the publication (for trail purposes) of two supplementary classifications: the International Classification of Procedures in Medicine (ICPM, published in two volumes in 1978); and the International Classification of Impairments, Disabilities, and Handicaps (ICIDH, published in 1980). In 1976, another classification, an extension of the neoplasm chapter of the ICD-9 was also published by WHO: the International Classification of Diseases for Onocology (ICD-O). Realizing that the ICD alone could not cover all the information required, at the first preparatory meeting for the Tenth revision, a new concept of a “family of disease and health-related classifications” was recommended.

US developments


For morbidity purposes in the United States, beginning with the ICD-7, a series of adaptations/modifications of the WHO publication were developed, each containing a section for the classification of procedures. The first was the International Classification of Diseases, Adapted for Indexing Hospital Records by Diseases and Operations, referred to as the ICDA (or sometimes, ICDA-7). This was followed by the Eighth Revision International Classification of Disease Adapted for Use in the United States (ICDA-8). (The latter was translated into French and published by Statistics Canada as CIMA-8.) The current US morbidity standard is the ICD-9-Clinical Modification (ICD-9-CM) which was implemented in 1979. Although the three classifications mentioned above were developed by or under the auspices of the US government, there were two successive modifications of the ICDA-8 produced by an independent organization, the Commission on Professional and Hospital Activities (CPHA) for use in its data abstracting system, the Professional Activity Study (PAS).

The current annual ICD-9-CM coordination and maintenance process is jointly controlled by two branches of the US government—the National Center for Health Statistics (NCHS) for the diagnosis component and the Health Care Financing Administration (HCFA) for the procedure component. The actual classification is published in a variety of formats by several independent publishing companies, each with its own unique features or variations. The ICD-9-CM has been adopted by some users outside the United States. Few countries have adopted it as their national morbidity standard, however. One recent exception (in 1992–93) was Australia. An Australian version/adaptation of ICD-9-CM is being published for implementation July 1, 1995.

Versions of ICD


The ICD-6, published in 1949, was the first to contain a section on mental disorders.


The ICD-9 was published by the WHO in 1977. According to the World Health Organization Department of Knowledge Management and Sharing, the WHO no longer publishes or distributes the ICD-9 which is now public domain.


International Classification of Diseases, Clinical Modification (ICD-9-CM) is a classification used in assigning codes to diagnoses associated with inpatient, outpatient, and physician office utilization in the U.S. The ICD-9-CM is based on the ICD-9 but provides for additional morbidity detail and is annually updated. It was created by the U.S. National Center for Health Statistics as an extension of ICD-9 system so that it can be used to capture more morbidity data and a section of procedure codes was added. This extension was called "ICD-9-CM", with the CM standing for "Clinical Modification".

It consists of two or three volumes:

The National Center for Health Statistics (NCHS) and the Centers for Medicare and Medicaid Services are the U.S. governmental agencies responsible for overseeing all changes and modifications to the ICD-9-CM.


Work on ICD-10 began in 1983 and was completed in 1992.The code set allows more than 155,000 different codes and permits tracking of many new diagnoses and procedures, a significant expansion on the 17,000 codes available in ICD-9.Adoption was relatively swift in most of the world. Some countries have created their own extensions. For example, Australia introduced their first edition of "ICD-10-AM" in 1998, and Canadamarker introduced "ICD-10-CA" in 2000.


Adoption of ICD-10 has been rather slow in the United States. Since 1988, the USA had required ICD-9-CM codes for Medicare and Medicaid claims, and most of the rest of the American medical industry followed suit.On 1 January 1999 the ICD-10 (without clinical extensions) was adopted for reporting mortality, but ICD-9-CM was still used for morbidity. Meanwhile, NCHS received permission from the WHO to create a clinical modification of the ICD-10, and has produced drafts of the following two systems:

  • ICD-10-CM, for diagnosis codes, is intended to replace volumes 1 and 2. A draft was completed in 2003.
  • ICD-10-PCS, for procedure codes, is intended to replace volume 3. A final draft was completed in 2000.

However, neither of these systems is currently in place. There is not yet an anticipated implementation date to phase out the use of ICD-9-CM. There will be a two year implementation window once the final notice to implement has been published in the Federal Register. A detailed timeline is provided here.

On August 21st, 2008, the US Department of Health and Human Services (HHS) proposed new code sets to be used for reporting diagnoses and procedures on health care transactions. Under the proposal, the ICD-9-CM code sets would be replaced with the ICD-10 code sets, effective October 1, 2013.


The first draft of the ICD-11 system (authored by WHO) is expected in 2010, with publication following by 2014 and in 2015+ implementation will take place. WHO has announced that it will apply Web 2.0 principles for the first time to revise the ICD. The ICD revision process is open to all comers willing to register, back their suggestions with evidence from medical literature and participate in online debate over proposed changes. More detailed information on the revision process and access to the revision platform is available at the WHO website.

Current use

ICD is the most widely used statistical classification system for diseases in the world. (See WHO official links.) Although some countries found ICD sufficient for hospital indexing purposes, many others felt that it did not provide adequate detail for diagnostic indexing. The original revisions of ICD also did not provide procedure codes for classification of operative or diagnostic procedures. As a result many countries developed their own adaptations of ICD.


United States

In the United States, hospitals and other healthcare facilities index healthcare data by referring and adhering to a classification system published by the U.S. Department of Health and Human Services: ICD, 9th Revision, Clinical Modification (ICD-9-CM). The Clinical Modification or CM system was developed and implemented in order to better describe the clinical picture of the patient. The CM codes are more precise than those needed only for statistical groupings and trend analysis. The diagnosis component of ICD-9-CM is completely consistent with ICD-9 codes.

ICD-10 was adopted in 1999 for reporting mortality, but the ICD-9-CM remains the data standard for reporting morbidity. Revisions of the ICD-10 have progressed to incorporate both clinical code (ICD-10-CM) and procedure code (ICD-10-PCS) with the revisions completed in 2003. Centers for Medicare and Medicaid Services has announced it will begin using ICD-10 on October 1, 2013.

Public data reporting

Mental and behavioral disorders

The ICD includes a section classifying mental and behavioral disorders. This has developed alongside the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders and the two manuals seek to use the same codes. There are significant differences, however, such as the ICD including personality disorders on the same axis as other mental disorders, unlike the DSM. The WHO is revising their classifications in these sections as part the development of the ICD-11 (scheduled for 2015), and an "International Advisory Group" has been established to guide this.

An important alternative to the mental disorders section of the ICD is the American Psychiatric Association's (APA) Diagnostic and Statistical Manual of Mental Disorders (DSM), which is the primary diagnostic system for psychiatric and psychological disorders within the United States and some other countries, and is used as an adjunct diagnostic system in other countries. Since the 1990s, the APA and WHO have worked to bring the DSM and the relevant sections of ICD into concordance, but some differences remain. An international survey of psychiatrists in 66 countries comparing use of the ICD-10 and DSM-IV found that the former was more often used for clinical diagnosis while the latter was more valued for research.


The years for which causes of death in the United States have been classified by each revision as follows:

  • ICD-1 - 1900
  • ICD-2 - 1910
  • ICD-3 - 1921
  • ICD-4 - 1930
  • ICD-5 - 1939
  • ICD-6 - 1949
  • ICD-7 - 1958
  • ICD-8A - 1968
  • ICD-9 - 1979
  • ICD-10 - 1999

See also


  1. WHO ICD-11 Revision information
  2. WHO adopts Wikipedia approach for key update
  6. WHO | International Classification of Diseases (ICD)
  7. N C H S - About the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM)
  8. [1]

External links

ICD 10

Principles & Practice Of ICD-10 Coding [2103]

Principles & Practice Of ICD-10 Coding in India [2104]

ICD-8 and earlier

WHO official ICD sites

USA modification official ICD-10 and ICD-9 sites

Other look up tools for ICD-10 and ICD-9

Conversion between ICD-9-CM-A and ICD-10-AM

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