HL7 ADT_A01 Admit/Visit Notification

The message that tells downstream systems a stay has started.
HL7 message structure ADT_A01 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
ROL
 Role No Yes
NK1
 Next of Kin / Associated Parties No Yes
PV1
 Patient Visit Yes No
PV2
 Patient Visit - Additional Information No No
ROL
 Role No Yes
DB1
 Disability No Yes
OBX
 Observation/Result No Yes
AL1
 Patient Allergy Information No Yes
DG1
 Diagnosis No Yes
DRG
 Diagnosis Related Group No No
ADT_A01.PROCEDURE
 Procedure group No Yes
PR1
 Procedures Yes No
ROL
 Role No Yes
GT1
 Guarantor No Yes
ADT_A01.INSURANCE
 Insurance group No Yes
IN1
 Insurance Yes No
IN2
 Insurance Additional Information No No
IN3
 Insurance Additional Information, Certification No Yes
ROL
 Role No Yes
ACC
 Accident No No
UB1
 UB82 No No
UB2
 UB92 Data No No
PDA
 Patient Death and Autopsy No No

ADT_A01 is the classic admission message. The patient has been admitted or the visit has been opened, and the patient administration system needs to tell nursing, pharmacy, lab, radiology, billing, dietary, bed management, clinical repositories, and interface engines that this patient is now active in the facility.

It is common, high-volume, and deceptively simple. The message is not just "a PID and a room." It is the start of a downstream identity, visit, location, clinical context, charging, and access-control story. If the A01 is wrong, later orders and results may be technically valid but attached to the wrong visit or account.

A small A01 example

MSH|^~\&|ADT|CITYHOSP|EHR|CITYHOSP|20260715103000||ADT^A01^ADT_A01|ADT00001|P|2.5.1 EVN|A01|20260715102930 PID|1||123456^^^CITYHOSP^MR||Smith^Jane^Anne^^Ms^^L||19800314|F|||12 High Street^^Auckland^^1010^NZ^H||^PRN^CP^^64^21^5551234 NK1|1|Smith^Robert|SPO|12 High Street^^Auckland^^1010^NZ^H|^PRN^CP^^64^21^5559876 PV1|1|I|WARD1^101^1^CITYHOSP^^BED||||12345^Careful^Clara|||||||||||VN000345^^^CITYHOSP^VN AL1|1||PEN^Penicillin^RXNORM|MO|Rash DG1|1||R07.9^Chest pain, unspecified^I10|||A GT1|1|G12345|Smith^Jane||12 High Street^^Auckland^^1010^NZ^H IN1|1|PLAN-A|INS001|City Health Plan

What systems do with it

The sender is normally the PAS, registration system, or ADT feed from an enterprise EHR. Receivers use it to create or update the patient and visit, open the account, assign a location, make the patient available for orders, and start eligibility or charging workflows. Some receivers need only PID and PV1; others require insurance, guarantor, diagnosis, allergy, and procedure groups.

When an A01 also creates an account, make the visit number, account number, and patient identifiers unambiguous. PID-3, PV1-19, and PID-18 are not interchangeable labels for the same thing.

How to read the structure

MSH identifies the message. EVN carries the trigger event and event timing. PID identifies the patient, while PV1 identifies the visit, patient class, location, attending doctor, and visit number. In most real A01 feeds those four segments are the backbone.

NK1, AL1, DG1, PR1, GT1, and IN1 often appear when the admission feed is also feeding patient accounting or clinical systems that need context before orders arrive.

Implementation traps

The biggest trap is sending an A01 for things that are not admissions. If the patient is only registered for an outpatient encounter, an A04-style workflow may be a better fit. If the patient is only pre-admitted, A05 is usually clearer. Receivers often route and store these differently.

Location updates also deserve care. A01 says the stay has started. Later bed changes should usually be A02 transfer messages. If every location correction is resent as A01, downstream systems can mistake a simple move for a fresh admission.

Reference notes

The HL7 v2+ refactored page for ADT_A01 describes A01 as an admitted-patient event and lists common downstream consumers such as pharmacy, nursing, finance, dietary, lab, radiology, and repositories. Local implementation guides may constrain the optional groups more tightly than the base structure.