ADT^A01 is the most common HL7 v2 trigger event. When a patient is admitted, the ADT system broadcasts this message to every subscribed system — lab, radiology, pharmacy, billing, EHR — so they all have current patient and visit information.
What is ADT^A01?
ADT stands for Admission, Discharge, and Transfer. The A01 event code signals a patient admission or visit notification. The message carries patient demographics (PID), event context (EVN), and visit location (PV1).
Sender: ADT system, HIS, or registration system (Epic ADT, Oracle Cerner, MEDITECH).
Receivers: Lab, Radiology, Pharmacy, Billing, EHR, Nursing, Bed Management.
When is ADT^A01 triggered?
- Formal inpatient admission — patient assigned to an inpatient bed after physician order
- Emergency to inpatient upgrade — ED patient converted to inpatient status
- Direct admit — patient admitted directly from physician’s office or clinic
- Observation status — patient placed under observation
Message Flow
Segments in this Message
Cardinality: [X] optional · {X} repeating · [{X}] optional & repeating
| Segment | Name | Required | Description |
|---|---|---|---|
MSH | Message Header | Required | Every HL7 message starts with MSH. Contains sending/receiving application, message type (ADT^A01^ADT_A01), timestamp, and unique message control ID used for deduplication. |
EVN | Event Type | Required | Records the event code (A01) and the event date/time. EVN-2 = recorded date; EVN-6 = event reason code. |
PID | Patient Identification | Required | Core patient demographics: MRN (PID-3), full name (PID-5), DOB (PID-7), gender (PID-8), address (PID-11), phone (PID-13). PID-3 is the identifier list — can carry MRN, SSN, and account number. |
PD1 | Additional Demographics | Optional | Patient's primary care provider and practice. PD1-4 carries the PCP's NPI and name in XCN format. |
NK1 | Next of Kin | Optional | Emergency contacts. Repeating — one NK1 per contact. NK1-2 = name, NK1-3 = relationship, NK1-5 = phone. |
PV1 | Patient Visit | Required | Visit details: patient class (I=Inpatient), bed location (PV1-3: ward^room^bed), attending physician (PV1-7), admit date (PV1-44), visit number (PV1-19). |
PV2 | Patient Visit – Additional | Optional | Extended visit info: expected LOS, visit description, patient condition. |
AL1 | Allergy Information | Optional | Active allergy list. Repeating — one AL1 per allergen. AL1-3 = allergen, AL1-5 = reaction, AL1-6 = onset date. |
DG1 | Diagnosis | Optional | Admitting diagnosis. DG1-3 = ICD-10 code and description. DG1-6 = diagnosis type (A=Admitting, W=Working, F=Final). |
HL7 Message Example
MSH|^~&|EPIC|MERCY|LABSYS|MERCY|20240115083042||ADT^A01^ADT_A01|MSG20240115001|P|2.5.1|||AL|NE
EVN|A01|20240115083042||ADT_EVENT|1234^JONES^DAVID^^^DR
PID|1||MRN-78234^^^MERCY^MR||SMITH^JOHN^ROBERT^^MR||19800315|M|||123 MAIN STREET^^BOSTON^MA^02101^USA^H||617-555-1234^PRN^PH
NK1|1|SMITH^JANE^MARY^^MRS|SPO^Spouse^HL70063|456 OAK AVE^^BOSTON^MA^02101|617-555-5678^PRN^PH
PV1|1|I|MICU^2B^01^MERCY||||1234^JONES^DAVID^R^^DR|||SUR||A|||IP-78234^^^MERCY^VN|||||||||||||||||||ADM|A0|||20240115083000
AL1|1|DA^Drug Allergy^HL70127|PENICILLIN^Penicillin||RASH|20100101
DG1|1||I10^Essential (primary) hypertension^I10|Essential hypertension|20240115|AFHIR Mapping
| HL7 Segment | FHIR Resource | Notes |
|---|---|---|
| PID | Patient resource | Official IG: ConceptMap-message-ADT_A01-to-bundle.json |
| PV1 | Encounter (status: in-progress) | Encounter.period.start = PV1-44 |
| DG1 | Condition resource | ICD-10 → CodeableConcept |
| NK1 | RelatedPerson | Relationship from HL70063 |
Official FHIR IG: https://build.fhir.org/ig/HL7/v2-to-fhir/ConceptMap-message-ADT_A01-to-bundle.json
Common Errors & Pitfalls
- Missing PV1-3 (patient location) — use ward^room^bed format. Required by most downstream systems.
- PID-5 name format errors — use XPN: LastName^FirstName^Middle. Do not put full name in a single field.
- PV1-44 admit date missing — required for billing. Use HL7 datetime: YYYYMMDDHHMMSS.
- MSH-9 two-part format — use three-part ADT^A01^ADT_A01 for v2.5+.
- No ACK handling — always wait for ACK before sending next message.
Vorro automatically deduplicates ADT^A01 messages using MSH-10 (message control ID). Configure per-destination dead-letter queues for failed deliveries. Use the field-mapping engine to normalize PV1-3 location codes across different ADT systems.
