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Terms and meanings in the terminology can be characterized by a point on a scale from very general to very specific. The degree to which the terminology includes highly specific terms is often referred to as granularity. More properly, terms can be said to be at a level that is coarsely granular, or at a level that is finely granular.

At upper levels, SNOMED CT accepts coarsely granular meanings that are useful only for aggregation and are not useful for individual patient data recording. Examples include clinical finding, procedure, measurement procedure, etc. Progressive levels of refinement are allowed to the extent required to meet clinical data requirements. There are, however, limits to the degree of precoordination of certain types of complex statements. There is a general rule that the terms in SNOMED CT should name things that exist in the real world, and therefore they should tend to be names or short noun phrases, not complete sentences and certainly not paragraphs. The terminology originated as a nomenclature, and it is intended to be used in concert with an information model that can carry full clinical statements along with their attribution, dates, times, and statement inter- Relationships. There is an evolving understanding of the boundary between items named in the terminology and more complex statements that should be represented as combined terminology-information elements.

More detailed advice and guidance can be found in the section "Content Inclusion: Principles and Process".

3.2.1 Grouper concepts i.e. used for grouping 

  • A grouping concept that can be fully defined and is determined to be clinically useful from a navigational perspective e.g. for an intensional reference set, may be added the the terminology with the following rules to be applied:
    1. These concepts are not created as navigational concepts. 

    2. These concepts use the semantic tag for the relevant hierarchy e.g. (Finding), (Procedure). 

    3. These concepts must not have stated subtypes. All subtypes must be inferred by the classifier. 

    4. Primitive grouping concepts cannot be added to the terminology, unless approved by the Head of Terminology 

    5. New grouping concepts will ONLY be added if they can be sufficiently defined.

  • Where existing grouping concepts exist, apply the criteria below: 

    1. If the grouping concept can be sufficiently defined, remodel and reassign existing subtypes to new proximal primitive parent. 
    2. If the grouper is currently primitive and cannot be sufficiently defined, identify for additional review.
  • Exceptions: Primitive grouping concepts cannot be added to the terminology, unless approved by the Head of Terminology with the following exception:

Where there are hierarchies which do not have a robust concept model, these may be added as primitive e.g. Genetic diseases. 



 If the addition of a grouping concept duplicates a concept in the navigational hierarchy (>>3363743006 | Navigational concept (navigational concept) |, the navigational concept shall be inactivated.