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 except.
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.