You can access LOINC content programmatically using the LOINC Terminology Service (TS). Our server uses the terminology services defined by HL7’s FHIR standard.

About the service

  • Service base URL: https://fhir.loinc.org
  • FHIR version: R4
  • LOINC version: 2.81
  • Additional versions of LOINC available via explicit request: 2.69, 2.70, 2.71, 2.72, 2.73, 2.74, 2.75*, 2.76, 2.77, 2.78, 2.79*, 2.80

*These versions contained known errors and were replaced by the subsequent version. We do not recommend accessing these version and they may be removed from this service in the future.

You need a LOINC login

All requests to LOINC’s terminology service require a LOINC username and password. If you do not already have a LOINC account, you may sign up for free.

Technical requirements for authentication are described separately.

BETA status

LOINC’s FHIR services have a BETA maturity status meaning that aspects of the implementation may change without notice and/or the services may not be be available 100% of the time. The is partly due to the fact that the FHIR standard itself is evolving. For these reasons, we do not recommend using this API in a production setting.

This Beta label is not to be confused with our content versioning designations. With the exception of LOINC Groups and Consumer Names, all content available from LOINC’s Terminology Service is production level and current with the latest LOINC release. At present, no pre-release terms are available from this API.

Using example requests

All provided examples will work within a web browser. You will need to provide your LOINC login information upon the first request of a session. We also suggest using the free Postman software as an API client.

You may copy each example URL and paste it into a browser window or within a Postman GET request. (As with the browser, you will need to provide your credentials using Postman’s Basic Auth option. See our separate authentication documentation.)

Known issues

  • Some previous versions of ConceptMap resources are not yet operational.
  • Expansion of select parent LOINC Group codes is failing.
  • Within the CodeSystem resource, some Radiology properties are duplicated on select terms, e.g. 36554-4. The terms for which there are duplicate properties are those that are mapped to multiple RPID codes in the LoincRsnaRadiologyPlaybook.csv file. Each LOINC-RPID mapping has its own set of rows for each of the Radiology attributes (properties) in the .csv file, so when a LOINC is mapped to more than one RPID, there will be multiple rows for each attribute. Because the Radiology properties in the FHIR representation are loaded from the .csv file, the multiple rows per attribute wind up as duplicates.

If you identify additional errors or issues, please use the methods below to contact us.

Questions and feedback

You can visit our Community Forum to discuss this server. If you notice something not working as expected, please let us know.

FHIR fundamentals

This primer will familiarize you on FHIR terminology concepts and how they are used within LOINC’s implementation. We will also let you know what you need to get started with this LOINC API and provided examples.

Resources

A FHIR resource is an individual specification for how to represent a particular concept related to healthcare. Currently more than 100 FHIR resources have been defined, including clinical (Medication, Immunization, Diagnosis), people or organizations (Patient, Provider), financial (Claim, Account), security (Provenance, AuditEvent), and terminology (CodeSystem, ValueSet).

Note that LOINC concepts are as codings in numerous resources. Use of LOINC in other resources is beyond the scope of this terminology service documentation.

FHIR terminology resources available in the LOINC TS:

  • CodeSystem: Describes key elements of a terminology (i.e., code system).
  • ValueSet: Identifies a set of codes from one or more code systems that is used for a specific purpose. LOINC Answer lists and LOINC Groups are examples of value sets provided by the LOINC FHIR terminology server.
  • ConceptMap: Defines a mapping between one or more concepts in one code system to one or more concepts in another code system. LOINC Part to SNOMED CT concept and LOINC term to RadLex Playbook concept are examples of concept maps.
  • Questionnaire: This resource is not required by HL7 for a terminology service but we include it due to LOINC’s wealth of standard assessments and survey content. The Questionnaire resource includes all child concepts (i.e. questions) and answer lists of a given assessment.

Operations

An operation is a command that specifies an action performed on a resource. Operations are prefixed with a dollar sign ($).

Select FHIR terminology operations:

  • $lookup: Returns information about a specific resource, such as a concept (e.g., LOINC term or Part), ValueSet (e.g., LOINC Answer list), or ConceptMap.
  • $expand: Returns the set of codes included in a ValueSet.
  • $validate-code: Checks to see if a specific code is in a given ValueSet.
  • $translate: Use with the ConceptMap resource to find all of the concepts a particular source concept is mapped to.

Parameters

A parameter is a structured way to pass input and output data for certain FHIR operations and interactions, especially in combination with operations.

Select FHIR terminology parameters:

  • property: Specific information about a resource. There are general properties defined across code systems (e.g., ), as well as specific properties defined within the LOINC code system (e.g., VersionFirstReleased, COMPONENT, ORDER_OBS, CLASSTYPE). Use with $lookup to return only the information related to that property.
  • designation: Designations within FHIR are described as additional representations of a given concept. They are used in the LOINC TS to provide non-English translations and alternate names. LOINC’s Linguistic Variants are provided as designations. Available translations are automatically returned on CodeSystem $lookup and ValueSet $expand operations. Other designations are Consumer Names and Short Names.

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