One of the fundamental benefits of SNOMED CT is its built-in polyhierarchy that specifies which concepts are subtypes of others. This hierarchy facilitates the automated grouping of health records which have been encoded using SNOMED CT. The relationships in SNOMED CT form the basis of its subtype hierarchy.
For example, has an
relationship to
, and therefore (as the diagram below illustrates), the concept
is subsumed by
.
Diagram uses notation from Diagramming Guideline. |
Example of subsumption |
This also means that if a patient has a , then it is implied (i.e. it is also true) that they have a
. We can use this principal to aggregate health records that have been encoded with SNOMED CT. By selecting any code that is a subtype of
, we are selecting all the codes that imply that
is true (given the appropriate context).
When testing for subsumption, we must also consider the transitivity of the
relationship. For example, the diagram below indicates that
is a subtype of
which is a subtype of
. Therefore
is also a subtype of
.
Example of subsumption and transitivity |
As previously suggested in the section 1.4. SNOMED CT Features, the hierarchical relationships of SNOMED CT can be leveraged to enable clinical decision support. More specifically, we can apply to make additional determinations. For additional information on subsumption, please refer to 6.2 Subsumptionin Data Analytics with SNOMED CT.
The diagram below shows a simple CDS rule based on the IF-condition-THEN-action pattern. This rule uses the descendant or self operator (<<) from the Expression Constraint Language - Specification and Guide to check if the diagnosis is in the set of concepts that includes and all of its subtypes.
CDS rule defined using subsumption |
When executing this rule, the inference engine tests if the given diagnosis is subsumed by the concept . This subsumption testing can be performed using a range of approaches, including using a 7.5.2 Transitive closure implementation. A transitive closure table facilitates rapid testing of all possible
relationships, and provides a very effective way of testing concept subsumption in relational databases.
The diagram below illustrates the process followed by the inference engine in executing the CDS condition in the above rule, when the clinician selects a diagnosis of . The inference engine checks if this concept is a subtype of
, and determines that it is. As a result, the condition evaluates to true, and the action is triggered.
The inference engine checks if the diagnosis entered is a subtype of |Asthma| |