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The  |LOINC Term to Expression reference set| is an instance of a  |Code to expression type reference set|.  The general specification of the reference set type is included below and this is followed by specific notes on the |LOINC Term to Expression reference set|.

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Specific Notes on the LOINC Term to Expression Reference Set

Rationale for Using a Code to Expression Type Reference Set

The |Code to expression type reference set| was designed to meet the known requirements for associating LOINC Terms with SNOMED CT expressions, in accordance with the terms of the cooperation agreement. The main reason for using expressions rather than OWL to represent the definitions, is that expressions can precisely represent all aspects of the definitions represented by SNOMED CT defining relationships. An additional factor was the relative human-readability of this format for review as demonstrated by the expression tab in the SNOMED International online browser (

LOINC Associations

Each LOINC Term Code within the scope of the cooperative work completed to date is associated with a SNOMED CT expressions that represent its formal logical definition. The definition is represented in accordance with the SNOMED CT concept model and thus each LOINC Term code in related directly to the SNOMED CT concepts that define it. The same definition could a expression to represent the definition. If a LOINC Term is recognized as having the same meaning as an existing SNOMED CT concept the associated expression may in future be supplemented by a direct map.

Expression Format

Each expression conforms to the SNOMED CT Composition Grammar. For further details of the syntax please see the  Compositional Grammar - Specification and Guide ( The expression represents the SNOMED CT definition of the LOINC Term based in the recently developed concept model for the  |Observable entity| domain. Note that the expression that represents a LOINC Term does not include any inferred relationships with other LOINC Terms. Furthermore, since the new  |Observable entity| has not yet been applied to many SNOMED CT concepts, the LOINC Terms are defined as subtypes  |Observable entity| with an appropriate set of attribute relationships.  Thus the expressions released in the beta release on 2017-03-31 included only stated relationships.

LOINC Term Code Status Changes

Deprecated statuses will cause the expression associations to be marked as inactive but trial use status will not be represented. LOINC Terms that were already deprecated at the time of initial mapping will not be included in maps and associations. However, dependent on demand and priority to assessments, it is possible these may be added later.

Values Specific to LOINC Term Expression Associations

The following values are used in this reference set.

Value for refsetId

Value for referencedComponentId

Values for contentOriginId

  705117003 |Originally in LOINC|  
705118008 |Originally in SNOMED CT|  
705119000 |Originally in both LOINC and SNOMED CT|

Other Values

All other values are as specified for the  |Code to expression type reference set|.


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