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 code, 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 (e.g., to process claims in medical billing based on diagnosis-related groups)
* knowledge-based and decision support systems
* direct surveillance of epidemic or pandemic outbreaks

There are country specific standards and international classification systems.

Classification types

Many different medical classifications exist, though they occur into 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 (known as ICD). 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 (I47.1) has the code title (rubric) '' 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 tachycardia listed 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
** They 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 (WHO) 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" (FIC) include three main (or reference) 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.

Reference classifications

*International Statistical Classification of Diseases and Related Health Problems (ICD)
**ICD-10 (10th revision, in use by WHO since 1994)
**ICD-11 (11th revision)
* International Classification of Functioning, Disability and Health (ICF)
* International Classification of Health Interventions (ICHI)

Derived classifications

Derived classifications are based on the WHO reference classifications (i.e. ICD and ICF). They include the following:

* '' International Classification of Diseases for Oncology'', Third Edition (ICD-O-3)
* ''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 (ICD-DA)
* ''Application of the International Classification of Diseases to Neurology'' (ICD-10-NA)
* 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:
* ICD-9-CM was the US' adaptation of ICD-9 and was maintained for use until September 2015. Starting on October 1, 2015, the Centers for Medicare and Medicaid Services (CMMS) granted physicians a one-year grace period to begin using ICD-10-CM, or they would be denied Medicare Part B claims.
* ICD-10-CM was developed by the US' Centers for Medicare and Medicaid Services (CMS) and the National Center for Health Statistics (NCHS), and has been in use in the US since October 2015replacing ICD-9-CM.
*ICD-10-AM was published by Australia's National Centre for Classification in Health in 1998 and has since been adopte