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Overview

Returns a single CodeSystem resource by its FHIR id. OMOPHub recognizes two ID shapes:
  1. Per-vocabulary stub IDs - short lowercase slugs (loinc, snomed, rxnorm, icd-10-cm, …) that map 1:1 to canonical FHIR system URIs. These return content: "not-present" stubs with metadata only.
  2. Unified OMOP release IDs - the release-specific FHIR id (e.g. omop-v20250827) for the omnibus OMOP CodeSystem that covers every supported vocabulary under one URL. These return the full CodeSystem resource with all OMOP property definitions.

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Request

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Per-vocabulary stub

curl "https://fhir.omophub.com/fhir/r4/CodeSystem/loinc" \
  -H "Authorization: Bearer YOUR_API_KEY"

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Unified OMOP release

curl "https://fhir.omophub.com/fhir/r4/CodeSystem/omop-v20250827" \
  -H "Authorization: Bearer YOUR_API_KEY"
Use the metadata endpoint to discover the current release ID, or call CodeSystem search with url=https://fhir-terminology.ohdsi.org to fetch the unified resource via the canonical URL.

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Response (per-vocabulary stub)

{
  "resourceType": "CodeSystem",
  "id": "loinc",
  "url": "http://loinc.org",
  "name": "LOINC",
  "title": "Logical Observation Identifiers Names and Codes",
  "status": "active",
  "experimental": false,
  "publisher": "Regenstrief Institute",
  "description": "Logical Observation Identifiers Names and Codes - served by OMOPHub. Use $lookup and $validate-code operations to query concepts; the full concept list is not served inline (content: not-present).",
  "content": "not-present"
}
Instance reads return a bare CodeSystem resource, not a Bundle. Only search-type queries wrap results in a Bundle.

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Response (unified OMOP release)

{
  "resourceType": "CodeSystem",
  "id": "omop-v20250827",
  "url": "https://fhir-terminology.ohdsi.org",
  "version": "2025.2",
  "name": "OMOPConcepts",
  "title": "OMOP Standardized Vocabularies",
  "status": "active",
  "date": "2025-08-27",
  "publisher": "OHDSI / OMOPHub",
  "description": "OMOP Standardized Vocabularies (release 2025.2). Served by OMOPHub at https://fhir.omophub.com. Content is identical to the OHDSI ATHENA vocabulary release.",
  "content": "not-present",
  "property": [
    {
      "code": "concept-id",
      "description": "The OMOP concept_id value for the concept.",
      "type": "integer"
    },
    {
      "code": "source-concept-code",
      "description": "The OMOP concept_code value as a FHIR Coding (includes system URI + code).",
      "type": "Coding"
    }
  ]
}
The full response lists every OMOP property and relationship type the server supports - see $lookup properties in the overview for the complete set.

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Why two shapes?

OMOPHub serves all 130+ vocabularies from a single unified backend. The per-vocab stubs are thin FHIR-conformant views over that backend, added so clients like HAPI and EHRbase can discover http://loinc.org as a first-class CodeSystem instead of having to know the OMOP omnibus URL. Both shapes resolve to the same concept data; pick whichever matches your client’s expectations.
Use the stub whenUse the unified CodeSystem when
A FHIR client is probing support by canonical URI (HAPI, EHRbase)You need release-specific metadata (version, release date, property definitions)
You want concise metadata for UI pickersYou’re building a client that walks OMOP properties directly
Round-tripping url: http://loinc.org from a search resultRound-tripping url: https://fhir-terminology.ohdsi.org

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Errors

HTTPIssue CodeCause
401loginMissing or invalid API key
404not-foundid does not match any known stub or released vocabulary version

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See Also