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Clinical information recorded using SNOMED CT may include data that is relevant to reports, statistical returns, billing claims, etc. that need to be encoded using a specific code system or a statistical classification such as ICD-10. Mapping allows relevant information to be used for those purposes, minimizing the requirement for additional manual data entry. 

There are a number of different types of mapping activities that an organization may need to undertake. These include mapping:

• SNOMED CT to a statistical classification (such as ICD-10)
• Classifications to SNOMED CT
• Other standard code systems to or from SNOMED CT
• Locally developed code systems to SNOMED CT
• Locally collected clinical data documented as free text to SNOMED CT

The completeness of mapping between two code systems depends on the scope, level of detail provided by the two code systems and the precision of mapping required to safely meet the intended mapping use case.

Maps are represented as reference sets, which are either of type ‘Simple map reference set’, ‘Complex map reference set’ or ‘Extended map reference set’ simple, complex and extended map reference sets. Special cases may also occur, which require ... a customized reference set to represent the map. An example of this is the 

705110001 | LOINC Term to Expression reference set |

...

• Maps from a single SNOMED CT concept to a combination of codes (rather than a single code) in the target scheme.
• Maps from a single SNOMED CT concept to choice of codes in the target scheme. In this case, the resolution of the choices may involve:
  • Manual selection supported by advisory notes.
  • Automated selection based on rules that test other relevant characteristics in the source data (e.g. age and sex of the subject, presence or absence of co-existing conditions, etc.).
  • A combination of automated processing with manual confirmation or selection where rules are insufficient to make the necessary decisions.

The completeness of mapping between two code systems depends on the scope, level of detail provided by the two code systems and the precision of mapping required to safely meet the intended mapping use case.

The figure below shows an except of some of the reference sets for maps between SNOMED CT and other code systems, which are available with the International Edition of SNOMED CT. However, local maps may also be developed and applied as part of an Extension to SNOMED CT.

Excerpt of mappings within the International Edition of SNOMED CT