OMOP to FHIR

The F2O translation also runs in reverse: given an OMOP standard concept_id, you can recover the source vocabulary codes (ICD-10-CM, SNOMED, RxNorm, …) that map to it. Echidna supports this via the OmopMappedFrom computed ConceptMap and via $expand with a relationship filter.

OmopMappedFrom — all source codes in one call

Pass the OMOP system URI and a standard concept_id to the OmopMappedFrom ConceptMap:

curl 'https://echidna.fhir.org/r4/ConceptMap/$translate?url=https://tx.echidna.systems/ConceptMap/OmopMappedFrom&system=https://fhir-terminology.ohdsi.org&code=201826'

Try it

This returns every source concept that has a Mapped from relationship to 201826 ("Type 2 diabetes mellitus"). For a broad standard concept like this, the response can be large — concept_id 201826 has 251 source concepts mapping to it, including ICD-10-CM E11.9 (35206882), ICD-9-CM 250.00, and many others.

Each match in the response carries equivalence relatedto and includes the source concept_id:

{
  "resourceType": "Parameters",
  "parameter": [
    { "name": "result", "valueBoolean": true },
    {
      "name": "match",
      "part": [
        { "name": "equivalence", "valueCode": "relatedto" },
        { "name": "concept", "valueCoding": {
            "system": "https://fhir-terminology.ohdsi.org",
            "version": "20260227",
            "code": "35206882",
            "display": "Type 2 diabetes mellitus without complications"
          }
        }
      ]
    }
  ]
}

Working with many sources

Reverse mapping is one-to-many by nature: a broad Standard concept can gather hundreds of source codes across many vocabularies (201826 has 251). Before consuming the result, decide what you actually need and filter accordingly:

• By vocabulary — if you only want, say, the ICD-10-CM sources, filter the returned matches on vocabulary-id rather than consuming all systems at once.
• By validity — some sources may be inactive or from retired releases; check inactive / invalid-reason if you need only currently valid codes.
• By specificity — the set mixes the exact concept with more specific descendants (for 201826, everything from "Type 2 diabetes mellitus" to complication-specific codes). Decide whether you want the precise equivalent only or the whole family.

For a narrower pull you can go straight to ValueSet/$expand with a Maps to filter plus a vocabulary-id filter, which does the filtering server-side instead of returning all 251 and filtering in your own code. Filters within an include are ANDed, so this returns only the ICD-10-CM sources for 201826:

curl -X POST 'https://echidna.fhir.org/r4/ValueSet/$expand' \
  -H 'Content-Type: application/fhir+json' \
  -d '{
    "resourceType": "Parameters",
    "parameter": [
      { "name": "valueSet", "resource": {
        "resourceType": "ValueSet",
        "compose": { "include": [ {
          "system": "https://fhir-terminology.ohdsi.org",
          "filter": [
            { "property": "Maps to",       "op": "=", "value": "201826" },
            { "property": "vocabulary-id", "op": "=", "value": "ICD10CM" }
          ]
        } ] }
      } }
    ]
  }'

Response (abridged — 3 of 74):

{
  "resourceType": "ValueSet",
  "expansion": {
    "total": 74,
    "contains": [
      { "system": "https://fhir-terminology.ohdsi.org", "code": "1326491", "display": "Type 2 diabetes mellitus with ketoacidosis" },
      { "system": "https://fhir-terminology.ohdsi.org", "code": "1326492", "display": "Type 2 diabetes mellitus with ketoacidosis without coma" },
      { "system": "https://fhir-terminology.ohdsi.org", "code": "1326493", "display": "Type 2 diabetes mellitus with ketoacidosis with coma" }
    ]
  }
}

Recovering the native source code

Requesting source-concept-code on a source concept returns its native code and system:

curl 'https://echidna.fhir.org/r4/CodeSystem/$lookup?system=https://fhir-terminology.ohdsi.org&code=35206882&property=source-concept-code&property=vocabulary-id'

Try it

Response (abridged):

{
  "resourceType": "Parameters",
  "parameter": [
    { "name": "code",    "valueCode":   "35206882" },
    { "name": "display", "valueString": "Type 2 diabetes mellitus without complications" },
    {
      "name": "property",
      "part": [
        { "name": "code",  "valueCode": "source-concept-code" },
        { "name": "value", "valueCoding": {
            "code":   "E11.9",
            "system": "http://hl7.org/fhir/sid/icd-10-cm"
          }
        }
      ]
    },
    {
      "name": "property",
      "part": [
        { "name": "code",  "valueCode": "vocabulary-id" },
        { "name": "value", "valueCode": "ICD10CM" }
      ]
    }
  ]
}

Note: carry the system through with the code. A bare E11.9 is ambiguous without its vocabulary URI, and downstream FHIR consumers need the system to build a valid Coding.