Medical classification in the context of "Nosology"

The International Classification of Diseases (ICD) is a globally used medical classification that is used in epidemiology, health management and clinical diagnosis. The ICD is maintained by the World Health Organization (WHO), which is the directing and coordinating authority for health within the United Nations System. The ICD was originally designed as a health care classification system, providing a system of diagnostic codes for classifying diseases, including nuanced classifications of a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease. This system is designed to map health conditions to corresponding generic categories together with specific variations; for these designated codes are assigned, each up to six characters long. Thus each major category is designed to include a set of similar diseases.

The ICD is published by the WHO and used worldwide for morbidity and mortality statistics, reimbursement systems, and automated decision support in health care. This system is designed to promote international comparability in the collection, processing, classification, and presentation of these statistics. The ICD is a major project to statistically classify all health disorders and to provide diagnostic assistance. The ICD is a core system for healthcare-related issues of the WHO Family of International Classifications (WHO-FIC).

The International Classification of Headache Disorders (ICHD) is a detailed hierarchical classification of all headache-related disorders published by the International Headache Society. It is considered the official classification of headaches by the World Health Organization, and, in 1992, was incorporated into the 10th edition of their International Classification of Diseases (ICD-10). Each class of headache contains explicit diagnostic criteria—meaning that the criteria include quantities rather than vague terms like several or usually—that are based on clinical and laboratory observations.

The ICHD was first published in 1988 (now known as the ICHD-1). A second version, the ICHD-2, was published in 2004. The most current version, ICHD-3, was published in 2018.

The classification of mental disorders, also known as psychiatric nosology or psychiatric taxonomy, is central to the practice of psychiatry and other mental health professions.

The two most widely used psychiatric classification systems are the International Classification of Diseases, 11th edition (ICD-11; in effect since 1 January 2022.), produced by the World Health Organization (WHO); and the Diagnostic and Statistical Manual of Mental Disorders produced by the American Psychiatric Association since 1952. The latest edition is the Fifth Edition, Text Revision (DSM-5-TR), which was released in 2022. The ICD is a broad medical classification system; mental disorders are contained in Chapter 06: Mental, behavioural or neurodevelopmental disorders (06).

ICD-10 is the 10th revision of the International Classification of Diseases (ICD), a medical classification list by the World Health Organization (WHO). It contains codes for diseases, signs and symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or diseases. Work on ICD-10 began in 1983, was endorsed by the Forty-third World Health Assembly in 1990, and came into effect in member states on January 1, 1993. ICD-10 was replaced by ICD-11 on January 1, 2022.

While WHO manages and publishes the base version of the ICD, several member states have modified it to better suit their needs. In the base classification, the code set allows for more than 14,000 different codes and permits the tracking of many new diagnoses compared to the preceding ICD-9. Through the use of optional sub-classifications, ICD-10 allows for specificity regarding the cause, manifestation, location, severity, and type of injury or disease. The adapted versions may differ in a number of ways; some national editions have expanded the code set even further, with some going so far as to add procedure codes. ICD-10-CM, for example, has over 70,000 codes.

The ICD-11 is the eleventh revision of the International Classification of Diseases (ICD). It replaces the ICD-10 as the global standard for recording health information and causes of death. The ICD is developed and annually updated by the World Health Organization (WHO). Development of the ICD-11 started in 2007 and spanned over a decade of work, involving over 300 specialists from 55 countries divided into 30 work groups, with an additional 10,000 proposals from people all over the world. Following an alpha version in May 2011 and a beta draft in May 2012, a stable version of the ICD-11 was released on 18 June 2018, and officially endorsed by all WHO members during the 72nd World Health Assembly on 25 May 2019.

The ICD-11 is a large ontology consisting of about 85,000 entities, also called classes or nodes. An entity can be anything that is relevant to health care. It usually represents a disease or a pathogen, but it can also be an isolated symptom or (developmental) anomaly of the body. There are also classes for reasons for contact with health services, social circumstances of the patient, and external causes of injury or death. The ICD-11 is part of the WHO-FIC, a family of medical classifications. The WHO-FIC contains the Foundation Component, which comprises all entities of the classifications endorsed by the WHO. The Foundation is the common core from which all classifications are derived. For example, the ICD-O is a derivative classification optimized for use in oncology. The primary derivative of the Foundation is called the ICD-11 MMS, and it is this system that is commonly referred to as simply "the ICD-11". MMS stands for Mortality and Morbidity Statistics. The ICD-11 is distributed under a Creative Commons BY-ND license.