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 (4.0.1)
- LOINC version: 2.83
- 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, 2.81, 2.82
*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 (including Special Use) 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
- None currently
If you identify errors or issues with this service, please 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
$lookupand ValueSet$expandoperations. Other designations are Consumer Names and Short Names.
Versioning
Previous versions of the LOINC terminology are available from this service. The list of available versions is referenced above. A version parameter must be supplied as part of the request to retrieve prior versions. If no version is provided, the current version of LOINC is returned.
This parameter name is version for CodeSystem, ConceptMap, and Questionnaire resources. ValueSet uses the valueSetVersion parameter.
Note that prior to the 2026-08-27 update of the LOINC Terminology Service, ConceptMap and ValueSet resources were versioned via a suffix on the URI. Prior to this update, previous versions of Questionnaire resources were not provided. The following ValueSet URIs are not available in versions previous to 2.83:
http://loinc.org/vs/deprecated-loinc-terms
http://loinc.org/vs/functional-status
http://loinc.org/vs/loinc-rsna-radiology-playbook-core
http://loinc.org/vs/loincs-for-sars-cov-2-aoe
http://loinc.org/vs/loincs-related-to-public-health-case-reporting
http://loinc.org/vs/top-lab-orders
http://loinc.org/vs/top-observations
http://loinc.org/vs/valid-hl7-attachment-requests
http://loinc.org/vs/valid-hl7-attachment-responses
http://loinc.org/vs/valid-hl7-attachment-responses-ig-exists
http://loinc.org/vs/valid-hl7-attachment-responses-no-ig-existsTable of Contents