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 groups diseases of the circulatory system into one "chapter," known as Chapter IX, 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:

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.[1] 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

Derived classifications

Derived classifications are based on the WHO reference classifications (i.e. ICD and ICF).[1] They include the following:

Related classifications in the WHO-FIC are those that partially refer to the reference classifications, e.g. only at specific levels.[1] They include:

Historic FIC classifications

ICD versions before ICD-9 are not in use anywhere.

ICD-9 was published in 1977, and was superseded by ICD-10. ICD-9-CM (Clinical Modification), was maintained for use in the US 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.[16]

The International Classification of Procedures in Medicine (ICPM) is a procedural classification that has not updated since 1989, and will be replaced by ICHI.[6] National adaptions of the ICPM includes OPS-301, which is the official German procedural classification.[17]

Other medical classifications


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:


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

National Drug File-Reference Terminology (NDF-RT)

National Drug File-Reference Terminology was a terminology maintained by the Veterans Health Administration (VHA). It groups drug concepts into classes. It was part of RxNorm until March 2018.

Medication Reference Terminology (MED-RT)

Medication Reference Terminology (MED-RT) is a terminology created and maintained by Veterans Health Administration in the United States. In 2018, it replaced NDF-RT that was used during 2005-2017. Med-RT is not included in RxNorm but is included in National Library of Medicine's UMLS Metathesaurus. Prior 2017, NDF-RT was included in RxNorm. The first release of MED-RT was in the spring of 2018.[20]

Medical Devices

  • Global Medical Device Nomenclature (GMDN), the standard international naming system for medical devices.[21]


Library classification that have medical components

ICD, SNOMED and Electronic Health Record (EHR)


The Systematized Nomenclature of Medicine (SNOMED) is the most widely recognised nomenclature in healthcare.[22] Its current version, SNOMED Clinical Terms (SNOMED CT), 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.[23] SNOMED CT is often described as a reference terminology.[24] SNOMED CT contains more than 311,000 active concepts with unique meanings and formal logic-based definitions organised into hierarchies.[23] 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.[23] SNOMED-CT is designed to be managed by computer, and it is a complex relationship concepts.[22]


The International Classification of Disease (ICD) is the most widely recognized medical classification maintained by the World Health Organization (WHO).[25] Its primary purpose is to categorise diseases for morbidity and mortality reporting. The United States has used a clinical modification of ICD (ICD-9-CM) for the additional purposes of reimbursement. ICD-10 was endorsed by WHO in 1990, and WHO Member states began using the classification system in 1994 for both morbidity and mortality reporting. In the US, however, it has only been used for reporting mortality since 1999. Because of the US delay in adopting its version of ICD-10, it is currently unable to compare morbidity data with the rest of the world. ICD has a hierarchical structure, and coding in this context, is the term applied when representations are assigned to the words they represent.[25] Coding diagnoses and procedures is the assignment of codes from a code set that follows the rules of the underlying classification or other coding guidelines.


SNOMED CT and ICD are designed for different purposes and each should be used for the purposes for which they were designed.[26] As a core terminology for the EHR, SNOMED CT provides a common language that enables a consistent language that enables a consistent way of capturing, sharing, and aggregating health data across specialties and sites of care. It is highly detailed terminology designed for input not reporting. Classification systems such as ICD-9-CM, ICD-10-CM, and ICD-10-PCS group together similar diseases and procedures and organise related entities for easy retrieval. They are typically used for external reporting requirements or other uses where data aggregation is advantageous, such as measuring the quality of care monitoring resource utilisation, or processing claims for reimbursement. SNOMED is clinically-based, documents whatever is needed for patient care and has better clinical coverage than ICD. ICD’s focus is statistical with less common diseases get lumped together in “catch-all” categories, which result in loss of information. SNOMED CT is used directly by healthcare providers during the process of care, whereas ICD is used by coding professionals after the episode of care. SNOMED CT has multiple hierarchy, whereas there is single hierarchy for ICD. SNOMED CT concepts are defined logically by their attributes, whereas only textual rules and definitions in ICD.

Data Mapping

SNOMED and ICD can be coordinated. The National Library of Medicine (NLM) maps ICD-9-CM, ICD-10-CM, ICD-10-PCS, and other classification systems to SNOMED.[27] Data Mapping is the process of identifying relationships between two distinct data models. The full value of the health information contained in an EHR system will only be realised if both systems involved in the map are up to date and accurately reflect the current practice of medicine.[25]

Clinical Coding in Australia

Medical coding and classification systems are expected to become increasingly important in the health care sector. Together with and as an integrated part of the electronic health information systems, the coding and classification systems will be used to improve the quality and effectiveness of the medical services.[28]

Clinical coding

Clinical coding is the translation of written, scanned and/or electronic clinical documentation about patient care into code format. For example, hypertension is represented by the code 'I10'; general anaesthesia is represented by the code '92514-XX[1910]'.

A standardised classification system, The International Statistical Classification of Diseases and Related Health Problems, 10th Revision, Australian Modification (ICD-10-AM), is applied in all Australian acute health facilities. It is based on the World Health Organization ICD-10 system, updated with the Australian Classification of Health Interventions (ACHI), Australian Coding Standards (ACS). Clinical coding is a specialised skill requiring excellent knowledge of medical terminology and disease processes, attention to detail, and analytical skills.[29]

A clinical coder is responsible for abstracting relevant information from the medical record and deciding which diagnoses and procedures meet criteria for coding as per Australian and State Coding Standards. The coder then assigns codes for these diagnoses and procedures based on ICD-10-AM conventions and standards.[29]


The assigned codes and other patient data are processed by grouper software to determine a diagnosis-related group (DRG) for the episode of care, which is used for funding and reimbursement. This process allows hospital episodes to be grouped into meaningful categories, helping us to better match patient needs to health care resources.[30]

The coded information is used for clinical governance, clinical audit and outcome and effectiveness of patient's care and treatment. Statistically this information is used to keep a track of payment by results, cost analysis, commissioning, etiology studies, health trends, epidemiology studies, clinical indicators and case-mix planning.

Veterinary medical coding

Veterinary medical codes include the VeNom Coding Group, the U.S. Animal Hospital Codes, and the Veterinary Extension to SNOMED CT (VetSCT).

See also


  1. "Family of International Classifications". World Health Organization. World Health Organization. Retrieved 12 July 2011.
  2. "International Classification of Diseases (ICD)". World Health Organization. World Health Organization.
  3. "ICD-10-CA". Canadian Institute for Health Information. Retrieved 12 July 2011. Archived 2015-05-01 at the Wayback Machine
  4. New Zealand Health Information Service. ICD-10-AM. Accessed 12 July 2011.
  5. "Family of International Classifications: definition, scope and purpose" (PDF). World Health Organization. World Health Organization. Retrieved 8 September 2015.
  6. "International Classification of Health Interventions (ICHI)". World Health Organization. World Health Organization. Retrieved 8 September 2015.
  7. "ICD-10-CM Release for 2014 now available". Dx Revision Watch. 2013-07-12. Retrieved 30 May 2015.
  8. "The ICD-10 Classification of Mental and Behavioural Disorders, Clinical descriptions and diagnostic guidelines" (PDF). World Health Organization.
  9. "The ICD-10 Classification of Mental and Behavioural Disorders, Diagnostic criteria for research" (PDF). World Health Organization.
  10. Bezroukov V (February 1979). "The application of the International Classification of Diseases to dentistry and stomatology". Community Dent Oral Epidemiol. 7 (1): 21–4. doi:10.1111/j.1600-0528.1979.tb01180.x. PMID 282953.
  11. van Drimmelen-Krabbe JJ, Bradley WG, Orgogozo JM, Sartorius N (November 1998). "The application of the International Statistical Classification of Diseases to neurology: ICD-10 NA". J. Neurol. Sci. 161 (1): 2–9. doi:10.1016/S0022-510X(98)00217-2. PMID 9879674.
  12. "ICPC-2". World Health Organisation.
  13. "ICECI". World Health Organisation.
  14. "Technical aids for persons with disabilities: Classification and terminology (ISO9999)". World Health Organisation.
  15. "International Classification for Nursing Practice (ICNP)". =World health organisation.
  16. "Get ready for the end of ICD-10 'flexibilities'". Modern Healthcare. Retrieved 2016-10-16.
  17. "OPS - German Procedure Classification". Archived from the original on 15 October 2015. Retrieved 8 September 2015.
  18. Olesen, Jes (2004). "The International Classification of Headache Disorders: 2nd edition". Cephalalgia. 24 (Suppl 1): 9–160. doi:10.1111/j.1468-2982.2003.00824.x. PMID 14979299. Archived from the original on 2013-01-05.
  19. Canadian Classification of Health Interventions. CCI.
  20. (PDF) Missing or empty |title= (help)
  21. IMDRF UDI Guidance Unique Device Identification (UDI) of Medical Devices 9.2.8.
  22. "SNOMED International". Retrieved 17 January 2017.
  23. "FAQs: Inclusion of SNOMED CT in the UMLS". Retrieved 17 January 2017.
  24. Office, Publications. "SNOMED CT - Systematized Nomenclature of Medicine". Retrieved 17 January 2017.
  25. Margret K. Amatayakul, MBA, RHIA, CHPS, CPHIT, CPEHR&FHIMSS.(2009).Electronic Health Records: A Practical Guide for Professionals and Organizations.Chicago, America:AHIMA
  26. "Why SNOMED cannot replace the ICD-10-CM/PCS code sets". Retrieved 17 January 2017.
  27. "WHO - SNOMED CT to ICD-10 Cross-Map Technology Preview Release". Retrieved 17 January 2017.
  28. Engum, B.; Solheim, B. G. (Feb 1994). "[Medical coding and classification systems]". Tidsskr nor Laegeforen. 114 (6): 694–6. PMID 8191453.
  29. "Clinical coding in Western Australia". Retrieved 17 January 2017.
  30. "Home - health.vic, Department of Health and Human Services, Victoria, Australia".
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