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The Root Concept

The Concept file includes a special conceptreferred to as the Root Concept. It is the "root" of the main hierarchy that contain all the Conceptsin SNOMED CT.

All other Conceptsare descended from this "root" conceptvia at least one series of Relationshipsof the Relationship Type 116680003 |is a|(i.e. all other Conceptsare regarded as subclasses of this Concept).

The Root ConceptCode is 138875005 |SNOMED CT Concept (SNOMED RT+CTV3)|and is named 138875005 |SNOMED CT Concept|.

Features of the root Concept

All other SNOMED CT Conceptsare subtypesof the root concept.

Unlike other SNOMED CT Concepts, the root conceptis not a subtypeof any other concept.

Release information in the root Concept

The root Concepthas a current Synonymthat contains information about the release. The Synonyms, representing earlier releases, are distributed as Inactive Descriptions. The release information is represented in the termtext of the Synonymas indicated in .

Table 4.1-1: Representation of release information in the root Concept


SNOMED Clinical Termsversion: 20020131 [R] (first release)


Stylized form

SNOMED Clinical Termsversion: yyyymmdd [ status] ( description)




The release date in ISOformat.



R (release), D (developmental) or E (evaluation).


An optional free text descriptionof the release.

Top-level Concepts

Conceptsthat are directly related to the Root Conceptby a single Relationshipof the Relationship Type 116680003 |is a|are referred to as "Top Level Concepts". All other conceptsare descended from at least one Top Level Conceptvia at least one series of Relationshipsof the Relationship Type 116680003 |is a|(i.e. all other conceptsrepresent subclasses of the meaning of at least one Top Level Concept).

Many Top-level Conceptsare intended to represent things outside of SNOMED CT(including processes, events, and material entities) in the real world. These include:

Table 4.1-2: Top Level Concepts

Representation of top-level Concepts

Awareness of the top-level Conceptsis likely to be particularly important when developing technical implementations.

A top-level Conceptcan be identified by the fact that it has a single subtype relationshipreferring to the Root Concept. However, to minimize processing requirements the top-level Conceptshave designated Concept Identifiersthat are documented in this guide as Important Concept Identifiers.

Top Level Metadata Concepts

Metadata codes represent structural information about the terminology itself. The Top Level Metadata Conceptsrepresent broad groups of metadata.

Table 4.1-3: Top Level Metadata

General Links

Core metadata concept

Foundation metadata concept