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Since the introduction of clinical information systems, clinical coding and clinical systems have acquired important roles in medical informatics. Over the years, classification and codification systems have evolved, not only to reduce software development, maintenance and processing time but also to become the heart of electronic medical records (EMRs).

  • Codes – are numeric or alphanumeric abbreviations that can expand into some meaning.
  • Nomenclature – An agreed system of assigned names.
  • Classification – Systematic representation of terms and concepts and the relationship between them.
  • Terminology – A set of words or expressions together with a definition used within a certain field.


Clinical classifications are useful in the areas of decision-making and research. They usually aim to be accurate, have unambiguous expressions and complete. In the UK, the British Association of Clinical Terminology Specialists (BACTS) ensures the quality of terminology development through its professional members.

The following are examples of clinical classification systems

  1. International Classification of Disease – 10 (ICD-10)International Classification of Disease is the oldest classification and is available worldwide. It is maintained by the World Health Organisation (WHO) and ICD-10 is the latest revision and came into use in April 1994. ICD-10 differs from the previous version (ICD-9) in that it has alphanumeric categories rather numeric categories. There is an ICD-10 homepage at the World Health Organisation site. A clinical modification of ICD-10 (ICD-10-CM) has been developed by the National Centre for Health Statistics (NCHS).
  2. Systematized Nomenclature of Medicine (SNOMED)SNOMED is a classification that is maintained by SNOMED International, a division of the College of American Pathologists (CAP). SNOMED’s design is based on detailed and specific nomenclature and has been successfully implemented internationally. The National Health Service in the UK has adopted a clinical version (SNOMED CT) as its preferred clinical terminology.
  3. NHS Clinical Terms (formerly READ Clinical Classification) - The READ Clinical Classification was designed by Dr James Read, a UK General Practitioner, for use by clinicians to cover the deficiencies that were not addressed by the already available codes. The UK’s National Health Service (NHS) purchased the READ codes in 1990 and since then many clinicians have been involved in the development of subsequent versions. The third version, which is also the latest, has a complete structural organisation with five hierarchical levels that takes advantage of modern day database technology. The READ Clinical Classification is still being used in the NHS, even though the NHS Executive has adopted SNOMED CT, as it preferred terminology.
  4. Logical Observation Identities, Names and Codes (LONIC) The LONIC database facilitates the exchange of laboratory results and the identification of clinical observations through a set of universal identifiers. The Regenstrief Institute maintains the LONIC database and its supporting documentation.
  5. Medical Subject Headings (MeSH) ThesaurusMeSH was developed by the National Library of Medicine (NLM) to create the INDEX MEDICUS, which is a scientific publications directory. MeSH has two categories of headings, which are arranged hierarchically. There are the Major MeSH headings, which are used for the description of the primary content of journals and the MeSH Headings, which describe the secondary content. The MeSH headings are published in a book called Medical Subject Headings – Annoted Alphabetic List. The headings are also used when accessing materials from the online medical journal database, MEDLINE.
  6. Unified Medical Language System (UMLS) – the National Library of Medicine (NLM) has developed UMLS since 1986. It has allowed healthcare professionals and researchers retrieve and integrate information from multiple electronic biomedical sources ranging from clinical records databases through directories of people and organisations to knowledge-based systems. UMLS is especially useful in overcoming multiple expressions of a single concept. The 11th edition of UMLS contains about three quarters of a million of such concepts, which map to MeSH, ICD-9-CM, SNOMED and other coding systems through its Metathesaurus. The UMLS Metathesaurus is just one of the components that make up the UMLS knowledge source. Some of the others include the Semantic Network, which provides a network of semantic types of all concepts represented in the Metathesaurus, and the Specialist Lexicon that contains linguistic information about biomedical and general English terms.
  7. North American Nursing Diagnosis Association (NANDA) Classification – The NANDA classification is a set of nursing diagnosis introduced by the North American Nursing Diagnosis Association (NANDA) in 1973. According to NANDA, the classification is based on "a selection of nursing interventions to achieve outcomes for which the nurse is accountable."



International Medical Informatics Association
American Medical Informatics Association
UK Health Informatics Society
British Computer Society Health Informatics Committee
European Federation for Medical Informatics
American Nursing Informatics Association
American Telemedicine Association

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Last Updated: 9 August 2006.

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