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The Root Concept

The Concept file includes a special concept referred to as the Root Concept. It is the "root" of the main hierarchy that contain all the Concepts in SNOMED CT.

All other Concepts are descended from this "root" concept via at least one series of Relationships of the Relationship Type 116680003 |is a|(i.e. all other Concepts are regarded as subclasses of this Concept).

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

Features of the root Concept

All other SNOMED CT Concepts are subtypes of the root concept.

Unlike other SNOMED CT Concepts, the root concept is not a subtype of any other concept.

Release information in the root Concept

The root Concept has a current Synonym that contains information about the release. The Synonyms, representing earlier releases, are distributed as Inactive Descriptions. The release information is represented in the term text of the Synonym as indicated in .

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


SNOMED Clinical Terms version: 20020131 [R] (first release)


Stylized form

SNOMED Clinical Terms version: yyyymmdd [ status] ( description)




The release date in ISO format.



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


An optional free text description of the release.

Top-level Concepts

Concepts that are directly related to the Root Concept by a single Relationship of the Relationship Type 116680003 |is a| are referred to as "Top Level Concepts". All other concepts are descended from at least one Top Level Concept via at least one series of Relationships of the Relationship Type 116680003 |is a|(i.e. all other concepts represent subclasses of the meaning of at least one Top Level Concept).

Many Top-level Concepts are 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 Concepts is likely to be particularly important when developing technical implementations.

A top-level Concept can be identified by the fact that it has a single subtype relationship referring to the Root Concept. However, to minimize processing requirements the top-level Concepts have designated Concept Identifiers that 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 Concepts represent broad groups of metadata.

Table 4.1-3: Top Level Metadata

General Links

Core metadata concept

Foundation metadata concept