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The haau3 Terminology API is a hosted FHIR R4 terminology service. It serves standard FHIR terminology operations over clinical code systems, so you can look up codes, expand value sets, and validate codes without running your own terminology server. It serves LOINC today, with more code systems to come.

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Operations

Three operations are available. Each requires a valid API key (see Authentication), and each returns the upstream FHIR resource as-is. See the API Reference for full parameters.
  • GET /v1/terminology/$lookup (FHIR CodeSystem/$lookup): look up a code and get its display and properties.
  • GET /v1/terminology/$expand (FHIR ValueSet/$expand): expand a value set to its member codes, with an optional text filter and paging.
  • GET /v1/terminology/$validate-code (FHIR ValueSet/$validate-code): check whether a code is a member of a value set.
A GET /v1/terminology/metadata endpoint returns the FHIR CapabilityStatement that declares these operations.

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Examples

Look up Hemoglobin A1c (4548-4): 
curl 'https://api.haau3.com/v1/terminology/$lookup?system=http://loinc.org&code=4548-4' \
  -H "Authorization: Bearer haau3_sk_…"
Expand the LOINC Hemoglobin A1c group, then validate that 4548-4 belongs to it: 
curl 'https://api.haau3.com/v1/terminology/$expand?url=http://loinc.org/vs/LG51070-7' \
  -H "Authorization: Bearer haau3_sk_…"
The url parameter is a value set canonical. It defaults to the implicit all-LOINC value set (http://loinc.org/vs). Pass a LOINC Group (http://loinc.org/vs/{LG-code}) or answer list (http://loinc.org/vs/{LL-code}) to scope to a specific set.

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Responses and errors

Responses are passed through from the upstream terminology server verbatim, as standard FHIR:
  • $lookup and $validate-code return a FHIR Parameters resource.
  • $expand returns a FHIR ValueSet with its expansion.
Status codes to expect:
  • 400: invalid query parameters, for example a missing code.
  • 401: missing or invalid API key.
  • 502: the upstream terminology server was unavailable or returned an error. Its FHIR OperationOutcome is included as outcome.
A code that is not in a value set is a successful 200 with "result": false in the Parameters, not an error.

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Code systems

The service proxies LOINC today (http://loinc.org), backed by LOINC’s official FHIR terminology server. Support for additional code systems, such as RxNorm, SNOMED CT, CVX, and HCPCS, is planned. For your first call, start with the Quickstart.