Medical classification

• International Statistical Classification of Diseases and Related Health Problems (ICD)[2]
  • 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) (in development[3][4])

Derived classifications are based on the WHO reference classifications (i.e. ICD and ICF).[1] 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 V of ICD-10,[5] and is available as two variants;
  • Clinical descriptions and diagnostic guidelines,[6] also known as the blue book.[5]
  • Diagnostic criteria for research,[7] also known as the green book.[5]
• Application of the International Classification of Diseases to Dentistry and Stomatology, 3rd Edition (ICD-DA)[8]
• Application of the International Classification of Diseases to Neurology (ICD-10-NA)[9]
• EUROCAT is an extension of the ICD-10 Chapter XVII, which covers congenital disorders.

Several countries have developed their own version of WHO-FIC publications, which go beyond a local language translation. The most notable are those based off 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.[10]
• 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 2015 – replacing ICD-9-CM.
• ICD-10-AM was published by Australia's National Centre for Classification in Health in 1998 and has since been adopted by a number of other countries.[11]

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

• International Classification of Primary Care (ICPC)[12]
  • ICPC-2 PLUS
• International Classification of External Causes of Injury (ICECI)[13]
• Anatomical Therapeutic Chemical Classification System with Defined Daily Doses (ATC/DDD)
• Technical aids for persons with disabilities: Classification and terminology (ISO9999)[14]
• International Classification for Nursing Practice (ICNP)[15]

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

ICD-9 was published in 1977, and was superseded by ICD-10. (ICD-10 is due to be replaced by ICD-11 on 1 January 2022.[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.[4] National adaptions of the ICPM includes OPS-301, which is the official German procedural classification.[17]

The categories in a diagnosis classification classify diseases, disorders, symptoms and medical signs. In addition to the ICD and its national variants, they include:

• Diagnostic and Statistical Manual of Mental Disorders (DSM)
  • DSM-IV Codes
  • DSM-5
• International Classification of Headache Disorders 2nd Edition (ICHD-II)[18]
• International Classification of Sleep Disorders (ICSD)
• Online Mendelian Inheritance in Man, database of genetic codes
• Read codes
• SNOMED CT

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 (ACHI)
• Canadian Classification of Health Interventions (CCI)[19]
• Chinese Classification of Health Interventions (CCHI)
• Current Procedural Terminology (CPT)
• Health Care Procedure Coding System (HCPCS)
• ICD-10 Procedure Coding System (ICD-10-PCS)
• OPCS Classification of Interventions and Procedures (OPCS-4)

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

• RxNorm
• Anatomical Therapeutic Chemical Classification System
• Medical Reference Terminology
• National Pharmaceutical Product Index

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) 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]

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

• Classification of Pharmaco-Therapeutic Referrals (CPR)
• Logical Observation Identifiers Names and Codes (LOINC), standard for identifying medical laboratory observations
• MEDCIN, point-of-care terminology, intended for use in Electronic Health Record (EHR) systems
• Medical Dictionary for Regulatory Activities (MedDRA)
• Medical Subject Headings (MeSH)
  • List of MeSH codes
• Nursing Interventions Classification (NIC)
• Nursing Outcomes Classification (NOC)
• TIME-ITEM, ontology of topics in medical education
• TNM Classification of Malignant Tumors
• Unified Medical Language System (UMLS)
• Victoria Ambulatory Coding System (VACS) / Queensland Ambulatory Coding System (QACS), Australia

• Dewey Decimal Classification and Universal Decimal Classification (section 610–620)
• National Library of Medicine classification

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. However the coded data is often used for other purposes too; including reimbursement practices such as medical billing. 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. The current version of the ICD, ICD-10, was endorsed by WHO in 1990. WHO Member states began using the ICD-10 classification system from 1994 for both morbidity and mortality reporting. The exception was the US, who only began using it for reporting mortality in 1999 whilst continuing to use ICD-9-CM for morbidity reporting. The US only adopted its version of ICD-10 in October 2015. The delay meant it was unable to compare US morbidity data with the rest of the world during this period. The next major version of the ICD, ICD-11, was ratified by the 72nd World Health Assembly on 25 May 2019, and member countries will be able to begin reporting data recorded using ICD-11 from 1 January 2022.[16]

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.

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 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.