^A04
ADT^A04 — Register a Patient
Sent when a patient is registered for an outpatient visit, emergency department encounter, or ambulatory appointment. Unlike A01 (inpatient admission), A04 is used when the patient is not assigned a bed or admitted inpatient.
When Is This Sent?
When a patient arrives and is registered at an outpatient clinic, ED, or ambulatory care setting. PV1.2 (patient class) will be O (outpatient), E (emergency), or R (recurring). Also used for pre-registration workflows.
Real-World Usage
A04 is often the highest-volume ADT message type in hospitals with large outpatient volumes. Many PACS systems need to receive both A01 and A04 to create imaging contexts for inpatient and outpatient patients respectively. If outpatient imaging orders aren't showing up in PACS, check whether A04 is being distributed to the PACS interface.
Message Structure
Segment names link to their field-level reference pages.
| # | Segment | Purpose in this message | Req | Repeat |
|---|---|---|---|---|
| 1 | MSH | Message header with ADT^A04 in MSH.9 | R | — |
| 2 | EVN | Event type with A04 trigger | R | — |
| 3 | PID | Patient demographics | R | — |
| 4 | PV1 | Visit information with PV1.2=O (outpatient) or E (emergency) | R | — |
| 5 | NK1 | Emergency contacts | O | Yes |
| 6 | PV2 | Extended visit information | O | — |
| 7 | AL1 | Patient allergies | O | Yes |
| 8 | DG1 | Reason for visit/diagnosis | O | Yes |
| 9 | IN1 | Insurance information | O | Yes |
Example Message
Realistic example with fake patient data. Paste into the HL7 Message Viewer to explore interactively.
1MSH||^~\&|EPIC|HOSPITAL_A|MIRTH_PROD|RIS|20260310090000||ADT^A04^ADT_A04|MSG00010|P|2.5.1 2EVN||A04|20260310090000 3PID||1||234567^^^HOSP_A^MR||Johnson^Sarah^L||19920601|F|||456 Oak Ln^^Springfield^IL^62702^US^H||2175559876^PRN^PH 4PV1||1|O|RADOUT^1^^HOSP_A||||5678^Wilson^Dr.^Sarah|||RAD||||REF|||||||OP||||||||||||||||||||||||||20260310090000
Troubleshooting Scenarios
Outpatient patients not appearing in PACS after registration
Cause
PACS interface is configured to only process A01 (inpatient admit) and is not receiving A04 (outpatient registration) messages.
Fix
Update the PACS interface channel to also process A04 events. Most PACS systems should handle both A01 and A04 identically for patient context creation.
Common Confusions
ADT^A04 (Register outpatient) vs ADT^A01 (Admit inpatient). The key difference is PV1.2: A01 typically has I (inpatient), A04 has O (outpatient) or E (emergency). Some EHR implementations send A04 for all encounter types regardless of patient class — always check PV1.2 rather than relying solely on the trigger event code.
Related Message Types
Segment Reference
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