HL7 ADT_A39 Merge Person - Patient ID

A deprecated patient-ID merge pattern that still appears in old feeds.
HL7 message structure ADT_A39 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
ADT_A39.PATIENT
 Patient group Yes Yes
PID
 Patient Identification Yes No
PD1
 Patient Additional Demographic No No
MRG
 Merge Patient Information Yes No
PV1
 Patient Visit No No

ADT_A39 is a backward-compatibility identity merge event. It was used when person records were incorrectly filed under different patient IDs. Current interfaces usually prefer the more explicit A40-style patient identifier list merge, but ADT_A39 still appears in local data and legacy systems.

Like every merge event, the operational risk is direction. The receiver must know which identifier survives and which prior identifier is being retired.

A small A39 example

MSH|^~\&|MPI|CITYHOSP|EHR|CITYHOSP|20260715152000||ADT^A39^ADT_A39|ADT390001|P|2.5.1 EVN|A39|20260715151900 PID|1||123456^^^CITYHOSP^MR||Smith^Jane^Anne^^Ms^^L||19800314|F MRG|999888^^^CITYHOSP^MR PV1|1|N

What systems do with it

The sender is usually a legacy MPI, registration master, or EHR identity component. Receivers reconcile prior identity data from MRG into the target patient carried in PID, but many modern systems translate or reject this event in favor of clearer merge messages.

How to read the structure

The local ADT_A39 structure has MSH, EVN, and one or more patient groups. Each patient group contains required PID and required MRG, with optional PD1 and PV1. The same backing structure is also useful for A40-style merge examples in this guide.

Implementation traps

Do not implement A39 without a site-specific rule for assigning authority, identifier type, and survivor direction. The event is deprecated in HL7 terminology, which is a strong hint to be conservative: accept it only when the trading partner has proved exactly what they mean.

Reference notes

HL7 terminology marks A39 as deprecated. The HL7 v2+ ADT_A39 structure page is also used for the A40 patient-identifier-list merge structure, so local implementations need to pay attention to both trigger event and message structure.