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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| SNOMED CT | 2/6 | https://en.wikipedia.org/wiki/SNOMED_CT | reference | science, encyclopedia | 2026-05-05T07:13:59.990399+00:00 | kb-cron |
Concept Codes – numerical codes that identify clinical terms, primitive or defined, organized in hierarchies Descriptions – textual descriptions of Concept Codes Relationships – relationships between Concept Codes that have a related meaning Reference Sets – used to group Concepts or Descriptions into sets, including reference sets and cross-maps to other classifications and standards. SNOMED CT "Concepts" are representational units that categorize all the things that characterize healthcare processes and need to be recorded therein. In 2011, SNOMED CT included more than 311,000 concepts, which are uniquely identified by a concept ID, e.g. the concept 22298006 refers to Myocardial infarction. All SNOMED CT concepts are organized into acyclic taxonomic (is-a) hierarchies; for example, Viral pneumonia IS-A Infectious pneumonia IS-A Pneumonia IS-A Lung disease. Concepts may have multiple parents, for example Infectious pneumonia is also a child of Infectious disease. The taxonomic structure allows data to be recorded and later accessed at different levels of aggregation. SNOMED CT concepts are linked by approximately 1,360,000 links, called relationships. Concepts are further described by various clinical terms or phrases, called Descriptions, which are divided into Fully Specified Names (FSNs), Preferred Terms (PTs), and Synonyms. Each Concept has exactly one FSN, which is unique across all of SNOMED CT. It has, in addition, exactly one PT, which has been decided by a group of clinicians to be the most common way of expressing the meaning of the concept. It may have zero to many Synonyms. Synonyms are additional terms and phrases used to refer to this concept. They do not have to be unique or unambiguous.
=== Semantic tag === SNOMED CT assigns each concept a semantic tag. It is present in parentheses in Fully Specified Name of each concept. There can be multiple semantic tags used within each SNOMED CT top level hierarchy. For example, top level hierarchy of Pharmaceutical/biologic Product uses semantic tags of: product, medicinal product, medicinal product form and clinical drug. Only one semantic tag can be used for each concept.
=== The formal model underlying SNOMED CT ===
SNOMED CT can be characterized as a multilingual thesaurus with an ontological foundation. Thesaurus-like features are concept–term relations such as the synonymous descriptions "Acute coryza", "Acute nasal catarrh", "Acute rhinitis", "Common cold" (as well as Spanish "resfrío común" and "rinitis infecciosa") for the concept 82272006. Under ontological scrutiny, SNOMED-CT is a class hierarchy (with extensive overlap of classes in contrast to typical statistical classifications like ICD). This means that the SNOMED CT concept 82272006 defines the class of all the individual disease instances that match the criteria for "common cold" (e.g., one patient may have "head cold" noted in their record, and another may have "Acute coryza"; both can be found as instances of "common cold"). The superclass (Is-A) Relation relates classes in terms of inclusion of their members. That is, all individual "cold-processes" are also included in all superclasses of the class Common Cold, such as Viral upper respiratory tract infection (Figure).
SNOMED CT's relational statements are basically triplets of the form Concept1 – Relationx – Concept2, with Relationx being from a small number of relation types (called linkage concepts), e.g. finding site, due to, etc. The interpretation of these triplets is (implicitly) based on the semantics of a simple Description logic (DL). E.g., the triplet Common Cold – causative agent – Virus, corresponds to the first-order expression
forall x: instance-of (x, Common cold) -> exists y: instance-of (y, Virus) and causative-agent (y, x)
or the more intuitive DL expression
Common cold subClassOf causative-agent some Virus
In the Common cold example, the concept description is "primitive", which means that necessary criteria are given that must be met for each instance, without being sufficient for classifying a disorder as an instance of Common Cold . In contrast, the example Viral upper respiratory tract infection depicts a fully described concept, which is represented in description logic as follows:
Viral upper respiratory tract infection equivalentTo Upper respiratory infection and Viral respiratory infection and Causative-agent some Virus and Finding-site some Upper respiratory tract structure and Pathological-process some Infectious process
This means that every individual disorder for which all definitional criteria are met can be classified as an instance of Viral upper respiratory tract infection.
=== Description logics === As of 2021, 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) General Concept Inclusion axioms (A ⊆ B). For understanding the modelling, it is also important to look at the stated view of a concept versus the inferred view of the concept. In further considering the state view, SNOMED CT used in the past a modelling approach referred to as 'proximal parent' approach. After 2015, a superior approach called "proximal primitive parent" has been adopted.
=== Precoordination and postcoordination === SNOMED CT provides a compositional syntax that can be used to create expressions that represent clinical ideas which are not explicitly represented by SNOMED CT concepts. This mechanism exists because it is challenging to create and maintain all possible concepts upfront (as precoordinated concepts). For example, there is no explicit concept for a "third degree burn of left index finger caused by hot water". However, using the compositional syntax it can be represented as
284196006 | burn of skin | : 116676008 | associated morphology | = 80247002 | third degree burn injury | , 272741003 | laterality | = 7771000 | left | , 246075003 | causative agent | = 47448006 | hot water | , 363698007 | finding site | = 83738005 | index finger structure