Perform IHE PIXm cross-reference patient identifiers using the $ihe-pix operation

Steps

1. Identify the PIXm Patient Identifier Cross-reference Manager actor endpoint; it exposes the $ihe-pix operation on the Patient resource type as defined in IHE PIXm v3.1.0 (transaction ITI-83)
2. Invoke the type-level operation: GET [base]/Patient/$ihe-pix?sourceIdentifier=<system>|<value> where sourceIdentifier is the known patient identifier in a specific domain (e.g., 'urn:oid:1.2.840.114350.1.13.0|MRN-12345')
3. Optionally add the targetSystem parameter to restrict returned identifiers to a specific domain: GET [base]/Patient/$ihe-pix?sourceIdentifier=<system>|<value>&targetSystem=<target-oid> to retrieve only the identifier in the target system
4. Parse the Parameters response resource: the server returns a Parameters resource with parameter elements named 'targetIdentifier' (each containing an Identifier for a cross-referenced domain) and 'targetId' (containing a FHIR Patient resource reference)
5. Use the returned cross-referenced identifiers to look up the patient in other systems or to populate the patient identifier field in a resource being submitted to another domain
6. Handle 'patient not found' (404) or 'identifier ambiguous' (OperationOutcome) responses by falling back to PDQm demographics query for patient matching