HL7 ADT_A24 Link Patient Information

Two identifiers are related, but their records are not merged.
HL7 message structure ADT_A24 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
EVN
 Event Type Yes No
PID
 Patient Identification Yes No
PD1
 Patient Additional Demographic No No
PV1
 Patient Visit No No
DB1
 Disability No Yes
PID
 Patient Identification Yes No
PD1
 Patient Additional Demographic No No
PV1
 Patient Visit No No
DB1
 Disability No Yes

ADT_A24 links patient identifiers that refer to the same person while keeping the underlying records distinct. That sounds subtle because it is. Link means "these records belong together for identity purposes"; merge means "one identifier or record should be absorbed into another."

A24 commonly appears in MPI and enterprise identity workflows where campuses, facilities, or source systems keep local records but need a broader patient identity relationship.

A small A24 example

MSH|^~\&|MPI|CITYHOSP|EHR|CITYHOSP|20260715142000||ADT^A24^ADT_A24|ADT240001|P|2.5.1 EVN|A24|20260715141900 PID|1||123456^^^CAMPUS-A^MR||Smith^Jane^Anne^^Ms^^L||19800314|F PV1|1|O|CLINIC1^12^1^CAMPUS-A PID|2||C987654^^^ENTERPRISE^EPI||Smith^Jane^Anne^^Ms^^L||19800314|F PV1|1|O|MPI^LINK^1^ENTERPRISE

What systems do with it

The sender is often an MPI or identity management service. Receivers use the repeated PID groups to record that two identifiers should be associated without deleting either record, overwriting local demographics, or moving clinical content automatically.

Patient portals, repositories, analytics, and cross-facility lookup systems may use this link so searches and patient matching work better across source systems.

How to read the structure

The local structure carries MSH, EVN, then two patient groups. Each group has required PID and optional PD1, PV1, and DB1. The repeated patient groups are the point of the message.

Implementation traps

Do not implement A24 as a merge. Records should remain distinct after the link. Also avoid using A24 for mother-baby linkage; HL7 has patient relationship fields and local newborn workflows for that, and the A24 reference explicitly warns against using this event for that purpose.

Reference notes

The HL7 v2+ ADT_A24 page describes linking two patient identifiers without requiring an actual merge, especially in MPI and multi-campus environments.