The International Classification of Diseases and other methods of classification of disease and medical care


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The international standard classification of disease is the International Classification of Diseases (ICD), published by the World Health organisation. [both accessed 16/08/2018]. It is periodically updated; the current version is ICD-11, released in June 2018  The ICD is divided into a series of chapters, such as 02 - neoplasms, 05 Endocrine, nutritional and metabolic diseases, 09 Diseases of the visual system, and 15 Diseases of the musculoskeletal (MSK) system or connective tissue.  Each individual disease is given a unique alpha numeric code. For example, Primary open-angle glaucoma is 9C61; a short description of glaucoma is given.


It is used to classify diseases and other health problems recorded on many types of health and vital records including death certificates and hospital records. In addition to enabling the storage and retrieval of diagnostic information for clinical and epidemiological purposes, these records also provide the basis for the compilation of national mortality and morbidity statistics by WHO Member States. In the UK it is used within the NHS when capturing diagnosis information in hospitals and is an important part of the identification of Healthcare Related Groups (HRGs) (see below) used for resource management and payment of providers. 


Enables international comparability in the collection, processing, classification, and presentation of these statistics.


New or emerging disease is not easily included without a major revision.  Each revision may lead to problems interpreting trend data.

Other methods of classifications

American Psychiatric Association's (APA) Diagnostic and Statistical Manual of Mental Disorders (DSM) is the primary diagnostic system for psychiatric and psychological disorders within the United States, the UK and many other countries. The latest version is DSM-5. [accessed 17/08/2018]. However, there have been criticisms of the new version

Since the 1990s, the APA and WHO have worked to bring the DSM and the relevant sections of ICD into concordance, but some small differences remain.

READ codes

Read codes, or Clinical Terms, were developed initially for use in primary care. They have a hierarchical structure describing the care and treatment of patients, including diagnosis, symptoms, tests and other interventions and can (mostly) be mapped to ICD10 and OPCS4. However, they have not generally been found easily usable at hospital levels, they are not always unique for a particular presenting condition (depending on the hierarchical sequence followed to arrive at the final code) and their ethnic categories do not correspond with those used elsewhere. Though they formed a major plank of an earlier NHS Information Strategy, they have not taken the place they were expected to. Read Version 2 and Clinical Terms Version 3 are due for retirement. “Information Standard Notices 1552 and 1553 confirmed the schedule for the retirement of Read v2 and v3 (CTV3) clinical terminologies. The last updated release of Read v2 was April 2016, and there will be no further update to CTV3 following the April 2018 release.”…….” Organisations should be well underway with their preparations to ensure they can use the dictionary of medicines and devices (dm+d) for medicines and SNOMED CT for clinical content.”  [accessed 17/08/2018]

SNOMED (Systematic Nomenclature of Medicine) is similar to Read codes but is more widely used in US.  A major project to combine SNOMED with the UK Read codes to form SNOMED-CT even in 2008 has not proved as successful as expected.  “SNOMED CT will go live in general practice care in a phased approach from April 2018.”

The International Classification of Functioning, Disability and Health (ICF) [accessed 17/08/2018]

ICF is an abbreviation of the International Classification of Functioning, Disability and Health. It describes health and health-related domains as body functions and structures, activities and participation. Because an individual's functioning and disability occur in a context, ICF includes a list of physical, social, attitudinal and environmental factors. Domains are classified from body, individual and societal perspectives. The classification places emphasis on function rather than condition or disease. It's designed to be applicable across cultures, age groups and gender, making ICF the basis for collecting reliable and comparable data on health outcomes for individuals and populations.

Implementing the classifications

The World Health Assembly approved ICF in May 2001 after a decade-long international revision process involving 65 different countries. ICF is designed for better, more uniform data for research and analysis. It will eventually be implemented worldwide, meaning that health and disability can be described and measured more effectively, and that the impact of these conditions can be monitored.


The Office of Populations, Census and Surveys (as it formerly was, before becoming part of the Office of National Statistics) produced classifications of operative interventions.  Within the UK these are standard codes used in hospital datasets to record surgical interventions. Along with ICD10 codes, they are used to derive HRG codes. The most recent release is Version 4.8,”…. due for implementation from April 2017.”  [accessed 17/08/2018]

OPCS4, which dates from 1992, is recognised as in need of revision. However, there has as yet been no consensus as to the best form of replacement. SNOMED-CT was expected to do this, but it is seen by many as not adequate for the purpose.

Healthcare Resource Groups (HRGs)

These are under the NHS National Casemix Office, which “…designs and refines classifications to describe NHS healthcare activity in England.”, of the US system of Diagnostic Related Groups (DRGs).

DRGs are used for payment of hospitals by health insurance organisations, and HRGs are used by the NHS to set standard reimbursements for care carried out. HRGs are intended to group cases of similar clinical character and similar resource use, and as such can be a valuable tool for public health analysts concerned with appropriate targeting and utilisation of NHS resources. They are regularly reviewed and updated, and are currently (2007-8) are version 4+.  Full details may be found.

[accessed 17/08/2018]




                                                 © M Goodyear & N Malhotra 2007, D Lawrence 2018