International Classification of Diseases (ICD)

• DATE: 1903 forward
• TYPE OF PSYCHOLOGY: Biological bases of behavior; psychopathology

The development of an international classification of diseases, beginning in the early twentieth century, provided a systematic method of organizing a statistical summary of organic disorders. Many of these illnesses have an impact on the biological basis for behavioral disorders.

Introduction

An understanding of the mathematical principles that underlay the existence and spread of disease in populations had its origins within the Royal Society of London during the seventeenth century. Founded in 1662, the Royal Society included among its members John Graunt, a local tradesman. Graunt collected and organized bills of mortality from local parishes, which represented the first complete listing of causes of morbidity and mortality in local populations. Descriptions were simplistic compared with data collected now; nevertheless, the principle that information about disease could be statistically compiled would lead to further refinements and increasing accuracy. In 1836, the establishment of the Registrar-General’s Office in London provided a central clearinghouse for compilation of such statistics. In particular, under the leadership of William Farr, compiler of statistical abstracts and finally superintendent, the office represented the first complete centralized bureau for analysis of disease in a population.

Farr initially divided diseases into five classes, three of the major groups being zymotic or infectious diseases; developmental diseases, such as those related to age or nutrition; and violent diseases. While some of Farr’s conclusions are obviously outdated, the separation of behavioral disease from those with clearly contagious characteristics represented an early attempt to distinguish the two.

The major impetus to categorizing morbidity or mortality statistics was the increasing level of information gathering within individual European countries. The development of the germ theory of disease provided a means of diagnosis for individual illnesses; as noted in several studies of the history of information technology, such growing medical statistics were a part of the larger quantification of everyday life in many of these Western countries.

As noted by information technologist Geoffrey Bowker, the International Statistical Institute (IST) during its 1891 meeting in Vienna established a committee under the auspices of Jacques Bertillon, chief of statistical works in Paris, to develop a system for the categorization of illnesses. At its meeting in Chicago two years later, the committee presented a system that was immediately adopted by the larger institute and that was implemented by most countries. The classification became known as the International Classification of Diseases, or ICD; the first system became known as ICD-1. The initial listing included two hundred categories, the number of lines present on the paper used by Bertillon’s committee during its deliberations.

Periodic Revision

As further refinements in research into diagnosis or understanding of disease came about, it was quickly clear that the original categories of illness would be insufficient as a universal classification system. Meetings at approximately ten-year intervals addressed such changes and resulted in significant revisions. The first major revision occurred in 1909 (ICD-2), the second in 1920 (ICD-3), and so on. Following World War I, the League of Nations became the governing body that dealt with the classification system.

At the International Health Conference that met in New York in 1946, the World Health Organization was charged with supervision of the system, including any necessary revisions; the result was ICD-6, which included nonfatal diseases such as those found in psychiatric disorders. In the years since, there have been periodic changes and revisions in that classification system; the ICD-10 was published in 1992, with the next revision, ICD-11, released in 2018 before being agreed upon for adoption in 2019 and going into effect in 2022. The full name of the publication became The International Statistical Classification of Diseases and Related Health Problems, although the common acronym of ICD-11 is still used. The number of classifications has ballooned, with more than 14,400 codes in the ICD-10 and with national Clinical Modifications sometimes including even more; the US clinical modification for the ICD-10, for example, had over 68,000. According to the WHO, the ICD-11 has approximately 55,000 unique codes. By May 2024, 132 member states were in the process of implementing ICD-11.

With development of computer technology, the use of numeric codes became standard in ICD classification. Among other changes, such a numeric system allowed for the encoding of more than just a single underlying cause of death on death certificates; contributing causes could also now be included. The result was a more accurate rendering of disorders affecting an individual. The ICD-11 marked the first time that the system was fully available electronically.

ICD Classification and Behavioral Disorders

ICD classification represents to a significant degree a classification system for causes of death. Its primary function is to track the changes in diagnosis and spread of disease in populations for epidemiological purposes. However, among the illnesses that have been included in the revisions since World War II are those that represent psychiatric and behavioral disorders.

The changes in the coding scheme in ICD-10 represented the most significant revision in the area of mental illnesses up to that point. In ICD-9, numeric codes numbered 001-999 were utilized. For the ICD-10 system, an alphanumeric scheme was adopted, which used a letter followed by a two-numeral character (A00-Z99). For example, Alzheimer’s disease as a cause of death was classified as G30 in the ICD-10 coding system. The coding of mental disorders increased from thirty categories in ICD-9 (290-319) to one hundred categories in ICD-10 (F00-F98). Each “family” of disorders represented a particular form or cause. For example, F00-F09 included only disorders with an organic basis. F10-F19 included “Mental and behavioral disorders due to psychoactive substance abuse,” and so on.

Some of these categories were further subdivided to allow for divisions within the form of the illness. For example, the category F60 represented “Specific personality disorders.” The category was subdivided into ten levels on the basis of specific forms or diagnoses of such disorders: F60.0 represented “Paranoid personality disorder,” F60.1 represented “Schizoid personality disorder,” and so on.

Changes in the ICD-11 included a simplification of the coding structure and new chapters such as "Diseases of the Immune System," "Sleep-Wake Disorders," and "Conditions Related to Sexual Health." A significant addition noted by the WHO and other experts was the inclusion of gaming disorder in the addictive disorders section, as was the addition of compulsive sexual behavior disorder. Also considered significant was ICD-11's redefinition of gender identity–related health, particularly with the transition to the inclusion of "gender incongruence" and its placement in the new chapter "Conditions Related to Sexual Health," instead of previously stigmatizing diagnostic categories; the WHO emphasized this change as one to ensure the accessibility of gender-affirming health care and insurance coverage for transgender people. At the same time, some LGBTQ activist groups argued that this change could still be further improved.

Bibliography

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Bowker, Geoffrey. “The Kindness of Strangers: Kinds and Politics in Classification Systems.” Library Trends, vol. 47, no. 2, 1998, pp. 255–92.

Ferenc, Debra P. Understanding Hospital Billing and Coding. 3rd ed. Elsevier, 2014.

ICD-11 Fact Sheet. World Health Organization, icd.who.int/en/docs/icd11factsheet‗en.pdf. Accessed 25 Oct. 2024.

"International Classification of Diseases (ICD)." World Health Organization, 2024, www.who.int/standards/classifications/classification-of-diseases. Accessed 25 Oct. 2024.

Killewo, J. Z. J., Kris Heggenhougen, and Stella R. Quah. Epidemiology and Demography in Public Health. Academic, 2010.

Lilienfeld, David, and Paul Stolley. Foundations of Epidemiology. 3rd ed. Oxford UP, 1994.

"Gender Incongruence and Transgender Health in the ICD." World Health Organization, 2024, www.who.int/standards/classifications/frequently-asked-questions/gender-incongruence-and-transgender-health-in-the-icd. Accessed 25 Oct. 2024.

"WHO Releases New International Classification of Diseases (ICD 11)." World Health Organization, 18 June 2018, www.who.int/news/item/18-06-2018-who-releases-new-international-classification-of-diseases-(icd-11). Accessed 25 Oct. 2024.