diff --git a/bus-gateway/controllers/iti67.js b/bus-gateway/controllers/iti67.js
index 68c1c6b..2f24cd0 100644
--- a/bus-gateway/controllers/iti67.js
+++ b/bus-gateway/controllers/iti67.js
@@ -20,20 +20,22 @@ function extractNationalIdentifier(patient) {
  * ITI-67: Find Document References (MHD)
  *
  * GET /fhir/DocumentReference?subject=:localId
+ * GET /fhir/DocumentReference?patient.identifier=:localId
  *
  * Flow:
  *   1. Fetch the Patient from the Bus by local ID to obtain the national identifier.
  *   2. Search DocumentReferences in the Bus by that national identifier.
  *   3. Return the resulting Bundle.
  *
- * Required query parameter:
- *   subject  — local Patient ID in the Bus.
+ * Required query parameter (one of):
+ *   subject            — local Patient ID in the Bus.
+ *   patient.identifier — same semantics, alternate FHIR parameter name.
  */
 async function listDocumentReference(req, res, next) {
     try {
-        const localPatientIdentifier = req.query.subject;
+        const localPatientIdentifier = req.query.subject ?? req.query['patient.identifier'];
         if (!localPatientIdentifier) {
-            throw createError(400, 'Missing required query parameter: subject');
+            throw createError(400, 'Missing required query parameter: subject or patient.identifier');
         }
         const token = await getBusToken(
             config.bus.url,