The most visible hierarchical construct in SNOMED CT is the subtype hierarchy. This is constructed using a set of logical rules.

Figure 27The subtype hierarchy

The primary use of the SNOMED CT subtype hierarchy is to support effective retrieval and aggregation of data.

Example:

The Concept "Laparoscopic emergency appendectomy" can be reliably located by subtype navigation from any of its supertypes: "appendectomy," "laparoscopic appendectomy" or "emergency appendectomy."

Enhanced Hierarchical Displays

It is possible to start at the top of hierarchy and navigate from parent to child in order to find a Concept or term in SNOMED CT. A more efficient approach, however, is to use the hierarchy to supplement a keyword search by enabling the user to look at related Concepts in order to consider them as alternative matches, or to check the context of a search result. The following examples illustrate these two uses of the SNOMED CT hierarchy.

Examples:

1. Checking supertypes:

A user wishes to find a Description that relates to the condition of a patient who is hypersensitive to an allergen. The user performs a search on the keyword "Hypersensitivity" and finds an exact match. Before the user selects the Description for inclusion in the patient record, they check the Fully Specified Name, which is | Sensitivity (finding) |. The user then checks the hierarchy and discovers that the selected Concept has | Psychological finding | as an ancestor, which indicates that this is not the correct Description to use in this context.

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