SNOMED CT

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SNOMED® (Systematized Nomenclature of Medicine), a system of standardized medical terminology, was developed by the College of American Pathologists(CAP). It began as a terminology system for pathology in 1965 and over the next 40 years evolved into SNOMED Clinical Terms®, or SNOMED CT®, a comprehensive computerized clinical terminology covering clinical data for diseases, clinical findings, and procedures. It is a “comprehensive and precise clinical reference terminology that provides unsurpassed clinical content and expressivity for clinical documentation and reporting.” [1] It allows a consistent way to index, store, retrieve, and aggregate clinical data across specialties and sites of care. [2] It also helps structure and computerize the medical record, reducing the variability in the way data is captured, encoded and used for clinical care of patients and research. [3] SNOMED created a common clinical language that is a necessary element of a health care Information Infrastructure. SNOMED® is a registered trademark of the College of American Pathologists. [4]

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[edit] Development

Clinicians and organizations use different clinical terms that mean the same thing. For example, the terms heart attack, myocardial infarction, and MI may mean the same thing to a cardiologist, but, to a computer, they are all different. Also, because of the need to exchange clinical information consistently between different health care providers, care settings, researchers, and others, and because medical information is recorded differently from place to place (on paper or electronically), a comprehensive, unified medical terminology system is needed. A medical terminology tool that can link multiple concepts and names systematically would allow clinical data to be communicated more clearly and accurately. [5]

In January 2002, SNOMED CT® was created by the merger, expansion, and restructuring of SNOMED RT® (Reference Terminology) and the United Kingdom National Health Service (NHS) Clinical Terms Version 3 (also known as the Read Codes). [6] The historical strength of SNOMED RT was its terminologies for specialty medicine, while the strength of Clinical Terms Version 3 was its terminologies for general practice. [7] By combining these two systems, SNOMED CT is the most comprehensive clinical vocabulary available in English (or any language), covering most aspects of clinical medicine with over 344,000 concepts. [8] SNOMED CT cross maps to such other terminologies as ICD-9-CM, ICD-O3, ICD-10, Laboratory LOINC and OPCS-4. It supports ANSI, DICOM, HL7, and ISO standards. [9] In April 2002, the SNOMED CT Spanish Edition was released, and in April 2003 the SNOMED CT German Edition was released.

As a controlled reference terminology it differs significantly from classification schemes. It is architected such that the content can be maintained as a dynamic resource, whereas classifications should be static. The release cycles have been six monthly.

Significant features of SNOMED CT by comparison with more traditional and familiar clinical terminologies (e.g. ICD) are primarily:

(1) It contains roughly 3 times as many concepts 'out of the box' as most familiar clinical terminologies

(2) The set of entities (or 'concepts') within its list are organised as a polyhierarchy rather than the traditional (statistical) monohierarchy

(3) Clinical end users can dynamically and arbitrarily extend the set of concepts within its list so as to include those additionally required but not already included in a particular release.

Local extension of SNOMED CT is achieved by defining new concepts as structured expressions of those already known. For example, a basic concept such as [burn] may be further qualified with a [severity] and a [body site], itself further qualifed, in order to define a new very detailed clinical concept such as a 'severe burn of the skin of the webspace between the left fourth and fifth toes':

 284196006|Burn of skin|:
   246112005|Severity|=24484000|severe,
   363698007|Finding Site|=
     (113185004|Structure of skin between fourth and fifth toes|:272741003|Laterality|=7771000|left)

Such expressions are said to have been 'post-coordinated' by contrast with the set of entities already included in a given SNOMED CT release, which are normally collectively labelled 'pre-coordinated' concepts, even though the majority (85%) of these pre-coordinated concepts are currently in fact primitive entities.

NB: in other contexts or projects 'coordination' may refer not to the specification of a candidate new expression but rather to the subsequent operation of integrating one within the polyhierarchy (ie classifying it). In SNOMED CT terminology, saying that an expression has been 'post-coordinated' does not imply that it has also been classified.

Reliable analysis and comparison of any such post-coordinated expressions - with respect to both those concepts already within the SNOMED CT release dataset and any other ad hoc concepts created or yet to be created by its community of endusers - properly requires the application of an appropriate description logic classification algorithm. As of 2007, SNOMED CT content limits itself to a subset of the EL++ formalism, restricting itself to the following operators:

top, bottom
primitive roles and concepts with asserted parent(s) for each
concept definition and conjunction but NOT disjunction or negation
role hierarchy but not role composition
domain and range constraints
existential but not universal restriction
a restricted form of role inclusion axiom (xRy ^ ySz => xRz)

The logic may be extended in the near future to include General Concept Inclusion Axioms.

In theory, description logic reasoning can be applied to any new candidate post-coordinated expressions in order to assess whether it is a parent or ancestor of, a child or other descendent of, or semantically equivalent to any existing concept from the 370,000 pre-coordinated concepts which are already distributed worldwide. However, partly as the continuing fall-out from the merger with CTV3, SNOMED content in 2007 still contains undiscovered semantically duplicate primitive and defined concepts. Additionally, many concepts remain primitive whilst their semantics can also be legitimately defined in terms of other primitives and roles concurrently in the system. Because of these ommissions and actual or possible redundancies of semantic content, real-world performance of algorithms to infer subsumption or semantic equivalence will be unpredictably imperfect.

SNOMED CT is expected to be adopted as an internationally maintained standard through the creation of The International Healthcare Terminology Standards Development Organisation (IHTSDO). This will see the principle intellectual property of SNOMED transferred to a Danish charity, with subsequent development funded exclusively by voluntary subscription by governments. Founder (Charter) members of the IHTSDO currently include Australia, Canada, Denmark, Lithuania, The Netherlands, New Zealand, Sweden, the United Kingdom, and the United States.

[edit] Sample Computer Applications Using SNOMED CT

  • Electronic Medical Records
  • Computerized Patient Order Entry Such As E-Prescribing Or Laboratory Order Entry
  • Remote Intensive Care Unit Monitoring
  • Laboratory Reporting
  • Emergency Room Charting
  • Cancer Reporting
  • Genetic Databases [10]

[edit] Basic Structure

  • Concepts: Basic unit of meaning designated by a unique numeric code, unique name (Fully Specified Name), and descriptions, including a preferred term and one or more synonyms.
  • Descriptions: Terms or names (synonyms) assigned to a concept.
  • Hierarchies: 19 higher level hierarchies; each has sub-hierarchies
  • Relationships: Link concepts either within a hierarchy or across hierarchies
  • Subsets

[11]

[edit] Use

SNOMED CT is one of a suite of designated data standards for use in U.S. Federal Government systems for the electronic exchange of clinical health information. The National Library of Medicine (NLM), on behalf of the U.S. Department of Health and Human Services, entered into an agreement with College of American Pathologists for a perpetual license for the core SNOMED CT (in Spanish and English) and ongoing updates. The contract provides to NLM a perpetual license to distribute SNOMED within the NLM’s Unified Medical Language System UMLS Metathesaurus for no cost use within the U.S. by both U.S. government (federal, state, local, and territorial) and private organizations. The contract also covers updates to SNOMED CT issued by the College of American Pathologists between June 30, 2003 and June 29, 2008.

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[edit] See also

[edit] References

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