Medical classification


A medical classification is used to transform descriptions of medical diagnoses or procedures into standardized statistical code in a process known as clinical coding. Diagnosis classifications list diagnosis codes, which are used to track diseases and other health conditions, inclusive of chronic diseases such as diabetes mellitus and heart disease, and infectious diseases such as norovirus, the flu, and athlete's foot. Procedure classifications list procedure codes, which are used to capture interventional data. These diagnosis and procedure codes are used by health care providers, government health programs, private health insurance companies, workers' compensation carriers, software developers, and others for a variety of applications in medicine, public health and medical informatics, including:
  • statistical analysis of diseases and therapeutic actions
  • reimbursement
  • knowledge-based and decision support systems
  • direct surveillance of epidemic or pandemic outbreaks
  • In forensic science and judiciary settings
There are country specific standards and international classification systems.

Classification types

Many different medical classifications exist, though they occur in two main groupings: Statistical classifications and Nomenclatures.
A statistical classification brings together similar clinical concepts and groups them into categories. The number of categories is limited so that the classification does not become too big. An example of this is used by the International Statistical Classification of Diseases and Related Health Problems. ICD-10 groups diseases of the circulatory system into one "chapter", known as Chapter, covering codes I00–I99. One of the codes in this chapter has the code title Supraventricular tachycardia. However, there are several other clinical concepts that are also classified here. Among them are paroxysmal atrial tachycardia, paroxysmal junctional tachycardia, auricular tachycardia and nodal tachycardia.
Another feature of statistical classifications is the provision of residual categories for "other" and "unspecified" conditions that do not have a specific category in the particular classification.
In a nomenclature there is a separate listing and code for every clinical concept. So, in the previous example, each of the listed tachycardias would have its own code. This makes nomenclatures unwieldy for compiling health statistics.
Types of coding systems specific to health care include:
  • Diagnostic codes
  • * Are used to determine diseases, disorders, and symptoms
  • * Can be used to measure morbidity and mortality
  • * Examples: ICD-9-CM, ICD-10, ICD-11
  • Procedural codes
  • * Are numbers or alphanumeric codes used to identify specific health interventions taken by medical professionals.
  • * Examples: CPT, HCPCS, ICPM, ICHI
  • Pharmaceutical codes
  • * Are used to identify medications
  • * Examples: ATC, NDC, ICD-11
  • Topographical codes
  • * Are codes that indicate a specific location in the body
  • * Examples :ICD-O, SNOMED, ICD-11

    WHO Family of International Classifications

The World Health Organization maintains several internationally endorsed classifications designed to facilitate the comparison of health related data within and across populations and over time as well as the compilation of nationally consistent data. This "Family of International Classifications" includes three main classifications on basic parameters of health prepared by the organization and approved by the World Health Assembly for international use, as well as a number of derived and related classifications providing additional details. Some of these international standards have been revised and adapted by various countries for national use.

Derived classifications

Derived classifications are based on the WHO reference classifications. They include the following:
  • International Classification of Diseases for Oncology, Third Edition
  • The ICD-10 Classification of Mental and Behavioural Disorders – This publication deals exclusively with Chapter of ICD-10, and is available as two variants;
  • *Clinical descriptions and diagnostic guidelines, also known as the blue book.
  • *Diagnostic criteria for research, also known as the green book.
  • Application of the International Classification of Diseases to Dentistry and Stomatology, 3rd Edition
  • Application of the International Classification of Diseases to Neurology
  • EUROCAT is an extension of the ICD-10 Chapter, which covers congenital disorders.

    National versions

Several countries have developed their own version of WHO-FIC publications, which go beyond a local language translation. Many of these are based on the ICD:
Related classifications in the WHO-FIC are those that partially refer to the reference classifications, e.g., only at specific levels. They include:
ICD versions before ICD-9 are not in use anywhere. ICD-9 was published in 1977, and superseded by ICD-10 in 1994. The last version of ICD-10 was published in 2019, and it was replaced by ICD-11 on 1 January 2022. 35 of the 194 member states have made the transition to the latest version of the ICD.
The International Classification of Procedures in Medicine is a procedural classification that has not updated since 1989, and will be replaced by ICHI. National adaptions of the ICPM includes OPS-301, which is the official German procedural classification.
International Classification of External Causes of Injury was last updated in 2003 and, with the development ICD-11, is no longer maintained. The concepts of ICECI are represented within ICD-11 as extension codes.

Other medical classifications

Diagnosis

The categories in a diagnosis classification classify diseases, disorders, symptoms and medical signs. In addition to the ICD and its national variants, they include:
The categories in a procedure classification classify specific health interventions undertaken by health professionals. In addition to the ICHI and ICPC, they include:
  • Australian Classification of Health Interventions
  • Canadian Classification of Health Interventions
  • Current Procedural Terminology
  • Health Care Procedure Coding System
  • ICD-10 Procedure Coding System
  • OPCS Classification of Interventions and Procedures

    Drugs

Drugs are often grouped into drug classes. Such classifications include:

SNOMED

The Systematized Nomenclature of Medicine is the most widely recognised nomenclature in healthcare. Its current version, SNOMED Clinical Terms, is intended to provide a set of concepts and relationships that offers a common reference point for comparison and aggregation of data about the health care process. SNOMED CT is often described as a reference terminology. SNOMED CT contains more than 311,000 active concepts with unique meanings and formal logic-based definitions organised into hierarchies. SNOMED CT can be used by anyone with an Affiliate License, 40 low income countries defined by the World Bank or qualifying research, humanitarian and charitable projects. SNOMED CT is designed to be managed by computer, and it is a complex relationship concepts.