The International Statistical Classification of Diseases & Related Health Problems (ICD) is the most commonly-used alternative to DSM - though it covers far more than just mental illness.

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. Under this system, every health condition can be assigned to a unique category and given a code, up to 6 characters long. Such categories can include a set of similar diseases.

ICD 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).

The ICD is revised periodically and is currently in its tenth edition. ICD-10 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 WHO.

History

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 10 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 when the classification system expanded to 2 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). After Bertillon’s death, 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 Organization 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 US 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 US Public Health Service later published the eighth revision. 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.

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 recognised, 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 trial purposes) of 2 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.

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.

ICD-6

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

ICD-9

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 in the public domain.

ICD-9-CM

International Classification of Diseases, Clinical Modification (ICD-9-CM) is a classification system used in assigning codes to diagnoses associated with in-patient, out-patient, and physician office utilisation in the US. The ICD-9-CM is based on the ICD-9 but provides for additional morbidity detail and is annually updated on October 1. It was created by the US 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.

It consists of two or three volumes:

· Volumes 1 and 2 contain diagnosis codes. (Volume 1 is a tabular listing and volume 2 is an index.)

· Volume 3 contains procedure codes.

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

ICD-10

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 version, ICD-10-AM in 1998, and Canada introduced ICD-10-CA in 2000.

ICD-10-CM

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.

Mental & Behavioural Disorders

The ICD includes a section classifying mental and behavioural disorders. This has developed alongside the American Psychiatric Association's Diagnostic & Statistical Manual of Mental Disorders and the 2 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.

DSM is the primary diagnostic system for psychiatric and psychological disorders within the United States and some other countries; and it 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

Godelief Willemse, Tom Van Yperen & Jan Rispens (2003) tested the reliability of ICD-10 for children’s disorders and found that, unless the category was objective, the reliability was poor -especially when the diagnosis was based on observations of the children.