Users can now retrieve LOINC content programmatically with a new terminology server via HL7®'s FHIR® API. Current LOINC content is available via a request to LOINC's FHIR server using the base URL of https://fhir.loinc.org. A free LOINC username and password is required to use the service.
To help get you started, we've written a primer covering the LOINC implementation of CodeSystem, ValueSet, and ConceptMap resources in FHIR. Additional documentation is also available in a presentation given recently by Dr. Vreeman at FHIR DevDays in Boston.
As an example, a developer may request information on an individual LOINC term (e.g. 4544-3) by making the following request to the CodeSystem endpoint:
https://fhir.loinc.org/CodeSystem/$lookup?system=http://loinc.org&code=4544-3
The response will be a structured definition of that code in JavaScript Object Notation (JSON) or Extensible Markup Language (XML) format. LOINC Parts, Answer Lists, and Answers are similarly available within this CodeSystem resource.
LOINC uses FHIR's ValueSet resource to define three types of code collections. Answer Lists and LOINC Groups are available upon demand, as are several key subsets including the LOINC Document Ontology and LOINC/RSNA Radiology Playbook. Through $expand and $validate-code operations, developers can get a list of codes within a particular value set or determine if an individual code exists within a defined collection.
Finally, FHIR's ConceptMap resource provides a means of programmatically mapping codes from LOINC to other code systems. For instance, the corresponding RPID within RadLex can be found via this request using the $translate operation:
https://fhir.loinc.org/ConceptMap/$translate?system=http://loinc.org&code=24706-4
Presently, LOINC's Terminology Server using FHIR carries a BETA status. The functionality may change and availability is not guaranteed. Regenstrief also cautions against using the server in a production context.