^A01
ADT^A01 — Admit/Visit Notification
Sent when a patient is admitted to a facility (inpatient) or begins a visit (outpatient). This is the first message in a patient encounter lifecycle and triggers downstream actions: bed assignment, order entry enablement, billing account creation, and clinical system access.
When Is This Sent?
When a patient is formally admitted to a healthcare facility. In practice, this fires when the admissions clerk completes the registration/admission workflow in the ADT system (HIS/EHR), typically after the patient arrives and a bed is assigned.
Real-World Usage
ADT^A01 is one of the highest-volume messages in any hospital. A 500-bed hospital typically generates 50-200 A01 messages per day. It triggers a cascade of actions across downstream systems: the PACS creates a patient context for imaging, the pharmacy enables medication ordering, the lab creates specimen collection records, and the billing system opens an account.
Message Structure
Segment names link to their field-level reference pages.
| # | Segment | Purpose in this message | Req | Repeat |
|---|---|---|---|---|
| 1 | MSH | Message header with ADT^A01 in MSH.9 | R | — |
| 2 | EVN | Event type with A01 trigger and timestamp | R | — |
| 3 | PID | Full patient demographics including MRN | R | — |
| 4 | PV1 | Visit information including patient class, assigned location, attending physician | R | — |
| 5 | PD1 | Additional demographics (primary care provider, advance directives) | O | — |
| 6 | NK1 | Next of kin and emergency contacts | O | Yes |
| 7 | PV2 | Extended visit information (expected discharge, admit reason) | O | — |
| 8 | AL1 | Patient allergies | O | Yes |
| 9 | DG1 | Admitting diagnosis | O | Yes |
| 10 | GT1 | Guarantor/responsible party information | O | — |
| 11 | IN1 | Insurance coverage information | O | Yes |
| 12 | IN2 | Extended insurance details | O | — |
Example Message
Realistic example with fake patient data. Paste into the HL7 Message Viewer to explore interactively.
1MSH||^~\&|EPIC|HOSPITAL_A|MIRTH_PROD|PACS|20260310143205||ADT^A01^ADT_A01|MSG00001|P|2.5.1 2EVN||A01|20260310143205 3PID||1||123456^^^HOSP_A^MR~987654321^^^SSA^SS||Smith^John^M^^Mr.||19850315|M|||123 Main St^^Springfield^IL^62701^US^H||2175551234^PRN^PH|||M 4PV1||1|I|4A^201^1^^^HOSP_A||||1234^Ahmed^Dr.^Khalid|||MED||||ADM|||5678^Wilson^Dr.^Sarah|IP||||||||||||||||||||||||||20260310143000
Troubleshooting Scenarios
Patient not appearing in downstream system after admission
Cause
MSH.5 (receiving application) doesn't match the downstream system's configured listener name, so the interface engine isn't routing the message to the right channel.
Fix
Check MSH.5 value against the receiving system's HL7 listener configuration. Many systems are case-sensitive. Also verify the channel filter in your interface engine is matching on ADT^A01 and not just ADT.
Patient admitted to wrong location in PACS or RIS
Cause
PV1.3 (assigned patient location) component mapping mismatch. The sending system sends UNIT^ROOM^BED but the receiving system expects FACILITY^UNIT^ROOM^BED.
Fix
Add a transformation in your interface engine to restructure PV1.3 components. Confirm the expected component order with the receiving system vendor. Document the location format for both systems in your interface specification.
Duplicate patient created instead of updating existing record
Cause
PID.3 (patient identifier list) format mismatch. The MRN assigning authority or ID type code doesn't match what the receiving system uses for patient matching.
Fix
Verify PID.3 components: ID^^^ASSIGNING_AUTHORITY^ID_TYPE. Ensure the assigning authority (component 4) and ID type (component 5) match exactly what the receiving system's patient matching algorithm is configured to use.
Common Confusions
ADT^A01 (Admit) vs ADT^A04 (Register). A01 is for inpatient admissions where PV1.2 = I. A04 is for outpatient visits, ED registrations, and ambulatory encounters where PV1.2 = O or E. Some EHR systems send A04 for all encounter types and never use A01 — your interface should handle both event types identically for most downstream systems.
Related Message Types
Segment Reference
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