Use the FHIR $validate-code terminology operation to verify that a code is valid within a specific ValueSet

In-depth guide

Steps

1. Send GET [base]/ValueSet/$validate-code?url=[valueSet-canonical]&system=[codeSystem]&code=[code] to the terminology server; alternatively POST with a Parameters body for more complex requests
2. Inspect the returned Parameters resource for the result parameter: a boolean true indicates the code is valid within the ValueSet, false indicates it is not
3. If result is false, read the message parameter for a human-readable explanation of why the code is invalid or not in the ValueSet
4. Optionally include display in the request to validate that the display string matches the code; the server returns a display parameter with the canonical display even if the submitted display differs
5. For FHIR resource validation workflows, call $validate-code for each coded element that must conform to a bound ValueSet before submitting the resource
6. Handle 400 errors for unknown code systems or ValueSets; check the OperationOutcome for whether the issue is an unknown system URL or an unsupported version