Please Note: This service will be unavailable on 20 July from 06:00 UTC till 18:00 UTC for essential maintenance.

SNOMED Documentation Search


 Other Documents

Versions Compared

Key

  • This line was added.
  • This line was removed.
  • Formatting was changed.

The use and representation of hierarchies in

Glossary ref
SNOMED CT
differs from the approach taken in many older code systems and classifications. This has a number of consequences that may affect the migration of queries, decision support protocols and data entry templates.

  • Anchor
    _87043b40-09f0-4a80-8a0f-12f688f72850__6
    _87043b40-09f0-4a80-8a0f-12f688f72850__6
    Meaningless
    Glossary ref
    Identifiers
    :
    Anchor
    _87043b40-09f0-4a80-8a0f-12f688f72850__f
    _87043b40-09f0-4a80-8a0f-12f688f72850__f
    • The codes specified in ICD-9,
      Glossary ref
      ICD-10
      , the
      Glossary ref
      Read Codes
      and
      Glossary ref
      SNOMED International
      provide information about where the code is located in a hierarchy. This allowed simple pattern matching queries to be used for some types of retrieval.

Example: In

Glossary ref
SNOMED International
, all 'diagnoses related to the digestive system' can be retrieved by a query for all codes starting with 'D5'
The
Glossary ref
Identifier
of a
Glossary ref
SNOMED CT concept
does not provide any information about the way it relates to other
Glossary ref
concepts
. Therefore, a simple pattern matching query cannot be used to retrieve related information represented using
Glossary ref
SNOMED CT
. Instead, the query that specifies a
Glossary ref
subtype
of the required
Glossary ref
concept
is evaluated by testing the
Glossary ref
transitive closure
of the set of
Glossary ref
subtype
Glossary ref
Relationships
.
Example: All 'diagnoses related to the digestive system' can be retrieved by a query for
Glossary ref
expressions
that are
Glossary ref
subtypes
of
Scg expression
ShowPartsid+term
119292006|disorder of gastrointestinal tract|
.

  • Polyhierarchy:
    Anchor
    _87043b40-09f0-4a80-8a0f-12f688f72850__8
    _87043b40-09f0-4a80-8a0f-12f688f72850__8
    • Glossary ref
      Statistical classifications
      and many other code systems have a
      Glossary ref
      monohierarchy
      in which each code falls within only one branch of the hierarchy. In contrast, the
      Glossary ref
      SNOMED CT
      Glossary ref
      subtype hierarchy
      is a
      Glossary ref
      polyhierachy
      , which means that each
      Glossary ref
      concepts
      can by a
      Glossary ref
      subtype
      of many different
      Glossary ref
      concepts
      . This is a powerful feature of
      Glossary ref
      SNOMED CT
      but it may significantly alter the results of a migrated from an earlier scheme.

Example: All 'diagnoses related to the digestive system' is some schemes may exclude codes that are primarily classified as infective disorders even they affect the digestive system. However, a

Glossary ref
SNOMED CT
query includes all
Glossary ref
subtype
Glossary ref
concepts
regardless of whether they are also in another hierarchy.

  • Different hierarchies:
    Anchor
    _87043b40-09f0-4a80-8a0f-12f688f72850__9
    _87043b40-09f0-4a80-8a0f-12f688f72850__9
    • Hierarchies in different code systems may be based on different principles and as a result queries that are migrated to
      Glossary ref
      SNOMED CT
      may return unexpected results. This may also relate to different interpretation of apparently identical
      Glossary ref
      concepts
      .

Example: Should a query for the

Glossary ref
concept
'nephrectomy' return only patients who have had a total nephrectomy or should the results include those with a record of a partial nephrectomy? If the partial nephrectomies are to be included then how much kidney tissue must be removed to count as a nephrectomy? If the partial nephrectomies are not included then should a record entry including the
Glossary ref
concept
'nephrectomy' (without specifying partial or total) be included? The
Glossary ref
SNOMED CT
Glossary ref
subtype hierarchy
determines the answer to these questions based on the defining
Glossary ref
Relationships
. The query may need to be refined to meet more specific expectations.