Look up a CodeSystem concept

$lookup finds a concept in a CodeSystem and returns information such as its preferred display, designations, and properties. Provide the code system and code directly, or pass them together in a Coding.

Method	Path
GET or POST	/fhir/R4/CodeSystem/$lookup

GET request

Use query parameters for a simple lookup. version, date, displayLanguage, and repeated property values can further constrain or shape the result.

curl --get 'https://api.sandbox.ovok.com/fhir/R4/CodeSystem/$lookup' \
  --header "Authorization: Bearer ${OVOK_TOKEN}" \
  --data-urlencode 'system=http://loinc.org' \
  --data-urlencode 'code=8867-4' \
  --data-urlencode 'displayLanguage=en'

POST request

Pass a Coding as a FHIR Parameters input when keeping the code system and code together:

curl --request POST \
  --url 'https://api.sandbox.ovok.com/fhir/R4/CodeSystem/$lookup' \
  --header "Authorization: Bearer ${OVOK_TOKEN}" \
  --header 'Content-Type: application/fhir+json' \
  --data @lookup-codesystem-parameters.json

Example lookup-codesystem-parameters.json:

{
  "resourceType": "Parameters",
  "parameter": [
    {
      "name": "coding",
      "valueCoding": {
        "system": "http://loinc.org",
        "code": "8867-4"
      }
    }
  ]
}

Successful response

The operation returns lookup details in a FHIR Parameters resource:

Response path	Example	Meaning
resourceType	Parameters	FHIR wrapper for the operation output.
parameter[name=name].valueString	LOINC	Name of the CodeSystem.
parameter[name=version].valueString	<code-system-version>	Version used for the lookup.
parameter[name=display].valueString	Heart rate	Preferred human-readable term.
parameter[name=designation].part	language=en, value=Heart rate	Alternate term and optional language or usage coding.
parameter[name=property].part	code=status, value=active	Typed concept property; properties may describe status, hierarchy, or terminology-specific details.

An unknown code or system is reported with a FHIR OperationOutcome.

Reference: HL7 FHIR R4 CodeSystem $lookup.