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A SNOMED CT Concept is a clinical idea to which a unique SNOMED CT identifier has been assigned.

Each Concept is associated with:

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Concept Identifiers

Each SNOMED CT Concept has a permanent unique numeric Identifier which is known as the Concept Identifier.

The sequence of digits in a Concept Identifier does not convey any information about the meaning or nature of the Concept [1 . The meaning of Concept is represented in human-readable forms by Descriptions and in a computer processable form by Relationships with other Concepts.

The advantages of meaningless Identifiers include:

  • Identifier permanence without undermining interpretation:
    • In contrast, to maintain consistency, a meaningful code may need to change to reflect revised understanding of the nature of a disorder ..
  • Enabling multiple aspects of meaning to be represented in the same way:
    • A meaningful code can only represent part of meaning of a complex concept. For example, |staphylococcal pneumonia| is an |infection|, a |respiratory disorder| and a |disorder| caused by |staphylococcus| but only one of these aspects can be represented by a code based hierarchy. Thus in the 'J' in the ICD-10 code 'J152: Pneumonia due to staphylococcus' represents that fact that this is a respiratory disorder but does not represent the fact that it is an infection (codes starting with 'A') or that it is due to staphylococcus ('A490: Staphylococcal infection, unspecified').
  • No artificial limitation on concept granularity:
    • Typical approaches to meaningful coding impose limits on both the number of levels of specificity (i.e. the length of the code) and the number of options at each level (i.e. the number of different symbols that can be used in each character position).

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Concept granularity

The meaning represented by a Concept can be general (for example 71388002 |procedure|), specific (for example 307996001 |excisional biopsy of lymph node|) or somewhere in between (for example 21911005 |biopsy of lymph node| ).

  • More specific Concepts:
    • Have finer granularity (more granular);
    • Represent clinical detail.
  • More general Concepts:
    • Have coarser granularity (less granular);
    • Represent less clinical detail;
    • Aggregate similar Concepts.

Support for multiple levels of granularity allows SNOMED CT to be used to represent clinical data at a level of detail that is appropriate to a range of different uses.

Concepts with different levels of granularity are linked to one another by 116680003 |is a|relationships. This enables appropriate aggregation of specific information within less detailed categories.

Figure 3.1.1-1: Multiple levels of granularity