Top Level Concepts

Hierarchy	138875005 \| SNOMED CT Concept (SNOMED RT+CTV3)\|
Purpose	The immediate subtype children of the root concept represent the most general types of SNOMED CT concepts.
Concept Addition Rules	It is strongly recommended that new top level concepts (i.e. direct subtype children of the root concept) are not added in an extension.
Additional Notes

Top Level Clinical Hierarchies

Hierarchies	All direct subtype children of 138875005 \| SNOMED CT Concept (SNOMED RT+CTV3)\| except 900000000000441003 \| SNOMED CT Model Component (metadata)\| .
Purpose	These concepts represent a distinct type of clinical concept
Concept Addition Rules	Subtype descendants of the top level clinical concepts may be added in an extension.
Additional Notes	Concepts added in these hierarchies should conform with: Concept model rules applicable to the relevant concept domain Quality standards applicable to all SNOMED CT clinical content. These concepts should be classified to generate a set of inferred relationships in necessary normal form, for inclusion in the extension distribution files.