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Clinical Terminologies
Medical (and indeed natural) language contains a number of properties that make it difficult to automate interpretation. Some medical terms are synonymous and need medical specialist knowledge to contextualise in each use. For example the term ‘cord compression’ could apply to both the spinal cord and the umbilical cord, and a computer application would not necessarily be able to distinguish which use or context was intended. Clinical terminologies are intended to be used by a clinician to enter data in a consistent format, to allow computerised exchange and retrieval. They address the fundamental problem that the same items of clinical information can be described in different ways, with groups or individual clinicians often having their own favourite terms or abbreviations, for example:
Myocardial infarction
Heart attack
Coronary thrombosis
MI
Myocardial infarct
All refer to the same concept, however when terms are examined in isolation, there is potential ambiguity. In this example the abbreviation “MI” could also refer to different concepts, and for some clinicians would be viewed as the default.
Mitral incompetence
Mesial incisal
Clinical terminologies address these problems by providing a defined set of terms, enabling consistency of data input, retrieval, communication and links to decision support. Terminologies code at a concept level, i.e. a single clinical entities such as diseases, observations, results and procedures.
Coverage varies between different terminologies, but most terminologies are organised in a hierarchy with upper level headings to cover relevant aspects of clinical and supporting information. These include administration, anatomical site, causes of injury, disorders, drugs and appliances, history and observations, investigations, prevention and operations and procedures.
The terminology provides a defined set of terms that are linked to appropriate medical concepts and are coded independently. Unique identifiers are provided for each concept and description and the relationships between them. A terminology therefore straddles the flexible, context-sensitive world of human language and the rigid, logical world of software. Main uses are:
Clinical data, capture and presentation Information integration, indexing and retrieval – linking clinical records, decision support.. Messaging between software systems Reporting
The components of a clinical terminology
The three basic components of a clinical terminology are:
Concepts, the basic units of thought, how humans perceive real world objects or events Terms, which describe concepts Codes, alternative labels which are machine processable, numeric or alphanumemeric
The relationship between concepts, terms and codes is sometimes referred to as the “semantic triangle”:
Concepts
The formal definition of a concept is “a unit of thought defined according to a set of attributes”, more simply it is the way we think about a real life object or event.
In the context of a clinical terminology, concepts can include:
Diseases Symptoms Observations Procedures Investigations
Term / Description
A term is the word used to describe the text string, word or phrase that the user uses to label the concept. These range from simple terms such as ‘hot’, ‘leg’, ‘lower limb’ to more complicated phrases like ‘failure of aortic valve’.
A Preferred term is the most commonly used or accepted term and a concept may have a number of synonyms. For example in the figure above the preferred term is ‘myocardial infarction’ while ‘heart attack’ is a synonym.
Codes Codes may represent concepts, term and the relationships between concept. They may be numeric (SNOMED CT) or text strings (Read codes). Originally codes served an additional purpose of space saving, however with the low cost and availability of storage space this is no longer an issue.
Clinical Terminology in the UK
In the UK, while there have been a number of terminologies, and there remain many custom developed single site coding schemes, At national level there are 3 main terminologies in use. Read codesThere are 3 versions of the Read codes The Four byte set was developed by Dr James Read, intended for use as in summary GP records. It has largely been superseded by Version 2 in primary care. Version 2 was developed for use in secondary care but ironically has had little adoption there, but is used in the majority of GP systems. A consequence of this is that there are a number of codes from the International Classification of Diseases (ICD) as in secondary these are used for central returns. This includes a number of somewhat obscure causes of accidents, including spacecraft and submarine accidents, that have little relevance to primary care, but do provide ongoing amusement or anger depending on one's attitude. CTV3 was developed as a single terminology for all sectors. It has much greater depth and consistency than Version 2 but has had relatively llittle uptake, although there has been more in the past 2 years. This is probably due to a combination of increased complexity and resistance to change. While Version 2 has numerous anomalies, mainly due to it's origin from ICD, GPs are familiar with it and it serves most of their purposes.
SNOMED Clinical Terms (SNOMED CT)
SNOMED CT was developed from 1999 to 2002 by the College of American Pathologists and the NHS Information Authority, as a merger between the existing SNOMED RT and CTV3 terminologists. Development is an ongoing iterative process involving diverse clinical groups and clinical informatics experts.
In 2007 SNOMED became open source under the auspices of the International Health Terminology Standards Development Organisation, based in Denmark. SNOMED CT is, in theory, mandated for the NHS National Programme for Information Technology. The first SNOMED enabled applications are just beginning to emerge, but it likely that there will be a mixed economy of terminologies in the UK for a few years.
Dictionary of Medicines and Devices (dm+d)
The NHS Dictionary of Medicines and Devices has been developed jointly by the NHS Information Authority and the NHS Prescription and Pricing Authority. It is intended for the dm&d to become the NHS standard for drug and device identification to support the National Programme for Information Technology, including the Integrated Care Record Service, and the Electronic Transfer of Prescription Service.
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It has been developed for use throughout the NHS (in hospitals, primary care and the community) as a means of uniquely identifying the specific medicines or devices used in the diagnosis or treatment of patients.
Specifically the purpose of the dm&d is to support:
Safe and reliable exchange of information on medicines Effective decision support through linkage of data Links to SNOMED CT Business process re-engineering of reimbursement of prescriptions Stock control and re-ordering Audit
The model has significant differences to SNOMED CT, although it containsSNOMED CT identifiers. Work is under way to 'SNOMEDise' dm+d |
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