HL7 ADT_A21 Patient Goes on a Leave of Absence

The patient leaves temporarily, but the admission is still alive.
HL7 message structure ADT_A21 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 Yes No
PV2
 Patient Visit - Additional Information No No
DB1
 Disability No Yes
OBX
 Observation/Result No Yes

ADT_A21 tells systems that an admitted patient has temporarily left the healthcare institution while the bed or episode remains active. It is a leave-of-absence workflow, not a discharge.

Receivers may pause meals, transport, inpatient services, or routine collections while preserving the admission, visit number, bed relationship, and future-return expectation.

A small A21 example

MSH|^~\&|ADT|CITYHOSP|EHR|CITYHOSP|20260715140000||ADT^A21^ADT_A21|ADT210001|P|2.5.1 EVN|A21|20260715135900||||20260715140000 PID|1||123456^^^CITYHOSP^MR||Smith^Jane^Anne^^Ms^^L||19800314|F PV1|1|I|WARD1^101^1^CITYHOSP^^BED||||12345^Ng^Grace|||||||||||VN000345^^^CITYHOSP^VN PV2|||||||||||||||||||||||||||||||||||||||||||||||20260717100000

What systems do with it

The sender is usually the PAS/EHR. Receivers mark the patient temporarily absent while keeping the active episode. Dietary, lab, pharmacy, transport, and bed systems may suppress or adjust tasks until the patient returns or the LOA is cancelled.

How to read the structure

The core is MSH, EVN, PID, and PV1. PV2 is where many profiles place expected return information. Optional DB1 and OBX are usually local additions.

For timing, pay attention to EVN-6 when populated. It can carry the time the patient actually left, which may differ from the time the event was recorded or transmitted.

Implementation traps

A21 should not close the visit. If downstream systems cancel orders, discharge the patient, or release the bed, they have treated a temporary absence as an end visit. Also make sure A52 cancel LOA and return-from-LOA workflows are supported if your trading partner sends them.

Reference notes

The HL7 v2+ ADT_A21 page describes leave of absence as a temporary departure while the bed remains assigned, with EVN-6 and PV2 expected-return timing called out.