The International Statistical Classification of Diseases and Related Health Problems (most commonly known by the abbreviation ICD) is a medical classification that provides codes to classify diseases and a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease. Under this system, 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 (WHO) 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).[1]
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[2] and will be revised using Web 2.0 principles.[3] Annual minor updates and triennial major updates are published by the WHO.[4] 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.
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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.[5] A number of countries and cities adopted Dr. Bertillon’s system, which was based on the principle of distinguishing between general diseases and those localized 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 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: 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. It later become clear that the established ten-year interval between revisions was too short.[5]
The ICD is currently the most widely used statistical classification system for diseases in the world. International health statistics using this system are available at the WHO Statistical Information System (WHOSIS).
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.
The ICD-6, published in 1949, was the first to contain a section on mental disorders.
The ICD-9 was finalized at the Conference for the Ninth Revision of the ICD in 1975[5] and published by the World Health Organization in 1977. It was eventually replaced by ICD-10, the version currently in use by the WHO and most countries. Given the widespread expansion in the tenth revision, it is not possible to convert ICD-9 data sets directly into ICD-10 data sets, although some tools are available to help guide users.[6]
International Classification of Diseases, Clinical Modification (ICD-9-CM) is an adaption created by the U.S. National Center for Health Statistics (NCHS) and used in assigning diagnostic and procedure codes associated with inpatient, outpatient, and physician office utilization in the United States. The ICD-9-CM is based on the ICD-9 but provides for additional morbidity detail. It is updated annually on October 1.[7][8]
It consists of two or three volumes:
The 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 the new revision was endorsed by the Forty-third World Health Assembly in May 1990. The latest version came into use in WHO Member States starting in 1994.[9] The classification system 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.[10] Adoption was relatively swift in most of the world. Several materials are made available online by WHO to facilitate its use, including a manual, training guidelines, a browser, and files for download.[1] Some countries have adapted the international standard, such as the "ICD-10-AM" published in Australia in 1998 (also used in New Zealand),[11] and the "ICD-10-CA" introduced in Canada in 2000.[12]
Adoption of ICD-10 has been slow in the United States. Since 1979[13], 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 production of all these systems:
On August 21, 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-CM code sets, effective October 1, 2013.[14]
ICD-10-CA is an enhanced version of ICD-10 developed by the Canadian Institute for Health Information for morbidity classification in Canada. ICD-10-CA applies beyond acute hospital care, and includes conditions and situations that are not diseases but represent risk factors to health, such as occupational and environmental factors, lifestyle and psycho-social circumstances.[12]
The final draft of the ICD-11 system is expected to be submitted to WHO's World Health Assembly (WHA) for official endorsement by 2015. The first (alpha) draft was made available online in July 2011 for initial consultation and commenting.[15]
The WHO is using Web 2.0 principles for the first time to revise ICD via a multi-author drafting platform known as the Initial ICD-11 Collaborative Authoring Tool (iCAT).[3] New features to ICD-11 include electronic health record readiness.[15]
In the United States, the U.S. Public Health Service published The International Classification of Diseases, Adapted for Indexing of Hospital Records and Operation Classification (ICDA), completed in 1962 and expanding the ICD-7 in 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, for official national morbidity and mortality statistics. This was followed by the ICD, 9th Revision, Clinical Modification, known as ICD-9-CM, published by the U.S. Department of Health and Human Services and used by hospitals and other healthcare facilities to better describe the clinical picture of the patient. The diagnosis component of ICD-9-CM is completely consistent with ICD-9 codes, and remains the data standard for reporting morbidity. National adaptations of the ICD-10 progressed to incorporate both clinical code (ICD-10-CM) and procedure code (ICD-10-PCS) with the revisions completed in 2003. In 2009, the U.S. Centers for Medicare and Medicaid Services announced that it would begin using ICD-10 on April 1, 2010, with full compliance by all involved parties by 2013.[10]
The years for which causes of death in the United States have been classified by each revision as follows:
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The ICD includes a section classifying mental and behavioral disorders (Chapter V). This has developed alongside the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM) 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.[16] 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.[17]