HL7 RSP_K23 Corresponding Identifiers Response

The identity source returns the other identifiers it knows for the person.
HL7 message structure RSP_K23 groups and segments from HL7 v2.5.1 Hide structure

These are the generated groups and segments for the version selected at the top of the page. The article explains the workflow, and this panel follows the chosen HL7 version.

Message Structure

SegmentNameRequiredRepeatable
MSH
 Message Header Yes No
SFT
 Software Segment No Yes
MSA
 Message Acknowledgment Yes No
ERR
 Error No No
QAK
 Query Acknowledgment Yes No
QPD
 Query Parameter Definition Yes No
RSP_K23.QUERY_RESPONSE
 Query Response group No No
PID
 Patient Identification Yes No
DSC
 Continuation Pointer No No

RSP_K23 is the response to a get-corresponding-identifiers query. A requester sends QBP_Q23 with a known patient identifier, and the receiver returns the matching identifiers from requested or configured domains.

This message is common in MPI and PIX-style environments where systems do not all share the same local MRN. The response is short, but the identifier semantics are serious. Most of the value lives in PID-3 and the assigning authority details inside each CX value.

A small RSP K23 example

MSH|^~\&|MPI|CITYHOSP|EHR|CITYHOSP|20260717101003||RSP^K23^RSP_K23|RSP230001|P|2.5.1 MSA|AA|QBP230001 QAK|Q230001|OK|Q23^Get Corresponding Identifiers^HL7nnn|1 QPD|Q23^Get Corresponding Identifiers^HL7nnn|Q230001|123456^^^CITYHOSP&1.2.3&ISO^MR|SOUTHLAB&2.16.840.1&ISO PID|1||123456^^^CITYHOSP&1.2.3&ISO^MR~SL998877^^^SOUTHLAB&2.16.840.1&ISO^MR||^^^^^^S

What systems do with it

The requester uses the returned identifiers to call another system, file incoming data under the right local patient, or build a crosswalk. An integration engine may query for the target system's ID before transforming and routing an order, document, or result.

QAK is where the receiver says whether the query found a useful answer. PID-3 is where the answer lives. A response with no corresponding IDs should be handled as a business outcome, not automatically retried like a transport failure.

How to read the structure

RSP_K23 contains the usual response header and status segments: MSH, MSA, optional ERR, QAK, and echoed QPD. The query-response group is lightweight: PID returns the identifiers, and optional continuation can follow if the profile permits paging.

Do not expect full demographics here. RSP_K23 is about corresponding identifiers. Some implementations include enough PID detail for safety, but the core contract is the identifier list.

Implementation traps

Never collapse all returned PID-3 repetitions into one local ID field. Each repetition belongs to a domain. Choose the domain you asked for, log the authority, and make the mapping rule visible.

Also make sure the response echoes the original query tag. Without that, requesters can mis-associate responses when multiple cross-reference queries are running at once.

Reference notes

IHE ITI-9 describes the PIX Query transaction as QBP^Q23 with RSP^K23, returning corresponding identifiers in PID-3 with fully qualified assigning authorities. See IHE ITI-9 and the HL7 Europe RSP_K23 message page.