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The International Statistical Classification of Diseases and Related Health Problems (commonly known by the abbreviation ICD) is a detailed description of known diseases and injuries. It is published by the World Health Organization and is used world-wide for morbidity and mortality statistics.

It is revised periodically and is currently in its tenth edition, known as the ICD-10.

Every disease (or group of related diseases) is described with its diagnosis and given a unique code, up to five letters long.

International Classification of Diseases

The International Classification of Diseases and Related Health Problems (commonly known by the abbreviation ICD) are designed to promote international comparability in the collection, processing, classification, and presentation of morbidity and mortality statistics. ICD-9. Commonly disputed by healthcare providers as billing code and not representative of true clinical outcomes, the ICD-9 transforms verbal descriptions of diseases, injuries, and procedures into numbers. The current ICD-9-CM has been revised to incorporate changes in the medical field. To date, there have been 10 versions of the ICD, with the ICD-10 developed in 1992 to track mortality statistics. 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 - 1992


The International Classification of Diseases (ICD) was designed to promote international comparability in the collection, processing, classification, and presentation of morbidity and mortality statistics.

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.

WHO published the ninth revision of ICD (ICD-9) in 1978. The U.S. Public Health Service modified ICD-9 to meet the needs of American hospitals and called it International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) [1]. The ninth revision expanded the book to three volumes and introduced a fifth-digit sub-classification.

Current Use

ICD has become the most widely used statistical classification system in the world. 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 for classification of operative or diagnostic procedures. As a result, interested persons in the United States began to develop their own adaptation of ICD for use 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: International Classification of Diseases, 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.

Of note, 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 progress to incorporate both clinical code (ICD-10-CM) and procedure code (ICD-10-PCS) with the revisions completed in 2003. However, ICD-9 has not been phased out by the new revision.

Public Data Reporting

Setting the data standard for healthcare providers for the world is a task undertaken in the last fifty years by the World Health Organization (WHO). As individuals become more involved in their personal healthcare, the data standard shared by most will be the International Classification of Diseases or ICD. These codes also have an active role in reporting of data from the Joint Commission on Accreditation of Healthcare Organizations JCAHO but also the current public data on hospitals released by the Centers for Medicare and Medicaid ServicesCMS in the United States


The ICD-9 was published by the WHO in 1977. At this time, the National Center for Health Statistics created an extension of it so the system could be used for morbidity as well as mortality ([2]). This extension was called "ICD-9-CM", with the CM standing for "Clinical Modification".

There are three volumes of the ICD-9-CM:


Work on ICD-10 began in 1983 and was completed in 1992. (Also see the ICD-10 online.)

Links to diseases can be accessed from: List of ICD-10 codes.

Adoption was relatively swift in most of the world, but not 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 January 1, 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. [3]. A detailed timeline is provided here.

Other countries have created their own extensions to ICD-10. For example, Australia introduced their first edition of "ICD-10-AM" in 1998, and Canada introduced "ICD-10-CA" in 2000.

See also

External links



Look up codes



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

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