In the context of RDF, OWL, and other technologies, URIs are the expected type of identifiers. Some LOINC users have asked for an approved convention for referring to LOINC-created identifiers (e.g. LOINC codes, LOINC Answer List Codes, LOINC Answer String Codes, etc). Here we describe approved patterns for use. Please note that this is an active area of discussion.

12.7.1 Using a URI to identify LOINC as a code system

In HL7 FHIR®, code systems are identified by URIs. As described in the section on LOINC as a code system, the recommended URI for this purpose is:

http://loinc.org

12.7.2 Using a URI to identify LOINC concepts as resources in RDF

The subject of an RDF statement is a uniform resource identifier (URI), or a blank node. After discussion at the Clinical LOINC Committee meeting in August 2015, we agreed to the following patterns:

For LOINC Terms:

http://loinc.org/rdf/{LOINC code}
e.g., http://loinc.org/rdf/2352-3

For LOINC Parts:

http://loinc.org/rdf/{LOINC Part code}
e.g., http://loinc.org/rdf/LP6990-8

In our current platform, URLs of these patterns resolve to the concept details pages (as used by search.loinc.org and RELMA).

Note: prior versions of the FHIR standard listed the preferred LOINC pattern as “http://loinc.org/owl“. The current version of FHIR has updated that guidance to be consistent with our recommendations in this document.

12.7.3 Using a URI to identify LOINC concepts as a value set

In some contexts, LOINC Parts, LOINC Answer Lists, and LOINC Groups represent value sets. LOINC represents the Component by System Hierarchy as a tree where LOINC Parts comprise all of the branches and LOINC terms comprise all of the leaf nodes. LOINC Answer Lists represent collections of coded concepts that can be used as response values to LOINC terms. LOINC Groups aggregate a set of LOINC terms that share certain characteristics. In these cases, LOINC defines an implicit value set associated with the code (e.g. a LP* code, a LL* code, or an LG* code).

Here we define a convention to make explicit when you are referring to these entities as either a) a code in the terminology or b) the implicit value set associated with the code.

When referencing the code itself, follow the usual pattern of referencing identifiers from the LOINC code system.

When referencing the implicit value set, use this pattern for the value set identifier as a URI: http://loinc.org/vs/{id}

For LOINC Parts:

http://loinc.org/vs/{LOINC Part code}
e.g., http://loinc.org/vs/LP148409-8

For LOINC Answer Lists:

http://loinc.org/vs/{LOINC Answer List code}
e.g., http://loinc.org/vs/LL715-4

For LOINC Groups:

http://loinc.org/vs/{LOINC Group code}
e.g., http://loinc.org/vs/LG9568-9