ADT^A04 — Register a Patient

The patient comes in for outpatient care or an ambulatory procedure, without immediate admission: A04 creates their record in the HIS and propagates to receivers.

Purpose

A04 registers a patient for an outpatient visit (consultation, ambulatory exam) or a procedure without admission. Unlike A01 which assumes a firm admission with a bed, A04 is lighter: no bed required, no length-of-stay, patient class O (Outpatient) or R (Recurring).

Typical use cases:

• outpatient clinic visit;
• ambulatory radiology exam;
• dialysis session, day-hospital chemo (recurring cycle);
• ER visit without admission (read-only, discharged same day).

Segment structure

A04 uses the same abstract structure as A01 (ADT_A01), with different PV1 values (PV1-2 = O, etc.).

ADT_A01 (reused for A04)
  MSH                    Message Header (mandatory)
  [ SFT ]                Software Segment (optional, R5+)
  EVN                    Event Type (mandatory)
  PID                    Patient Identification (mandatory)
  [ PD1 ]                Patient Additional Demographics
  [ { ROL } ]            Role
  [ { NK1 } ]            Next of Kin
  PV1                    Patient Visit (mandatory) — PV1-2 = 'O' typically
  [ PV2 ]                Patient Visit - Additional Info
  [ { ROL } ]
  [ { DB1 } ]            Disability
  [ { OBX } ]            Observation/Result (reasons, arrival vitals)
  [ { AL1 } ]            Patient Allergy Information
  [ { DG1 } ]            Diagnosis (consultation reason)
  [ DRG ]                Diagnosis Related Group
  [ { PR1 [ { ROL } ] } ] Procedure
  [ { GT1 } ]            Guarantor
  [ { IN1 [IN2] [IN3] } ] Insurance
  [ ACC ]                Accident
  [ UB1 | UB2 ]
  [ PDA ]

MSH — Message Header

• MSH-9: ADT^A04^ADT_A01.
• MSH-12: 2.5.1.

EVN — Event Type

• EVN-1: A04.
• EVN-2: entry date/time.
• EVN-5: operator (front desk).

PID — Patient Identification

Identical to A01. Critical for identity vigilance.

PV1 — Patient Visit

• PV1-2: patient class. For A04: O (Outpatient), R (Recurring), E (Emergency no admit).
• PV1-3: location (office, consultation room), not necessarily a bed.
• PV1-4: admission type (R=Routine).
• PV1-7: attending physician (often the consultant).
• PV1-18: patient type (OUT).
• PV1-19: visit number (stay key).
• PV1-44: registration date/time.

Real-world example

Patient Anne Martin, MRN789012, registered for an outpatient cardio consultation with Dr Bernard:

MSH|^~\&|HIS|HOSP01|EHR|CLINIC02|20260515082030||ADT^A04^ADT_A01|MSG00003001|P|2.5.1|||AL|NE
EVN|A04|20260515082030|||OPSEC^Operator^Front Desk
PID|1||MRN789012^^^HOSP^MR||MARTIN^ANNE^E^^MS.||19850612|F|||45 MAIN ST^^NEW YORK^NY^10001^USA||(555)478-3344|||S||ACCT789012
PV1|1|O|CONS^CONS01^^HOSP01|R|||DRBERNARD^Bernard^Philippe^^^DR.|||CAR|||1||||OUT||||||||||||||||||HOSP01|||||20260515082030

Acknowledgment (ACK)

MSH|^~\&|EHR|CLINIC02|HIS|HOSP01|20260515082031||ACK^A04^ACK|ACK00003001|P|2.5.1
MSA|AA|MSG00003001

A01 vs A04

Common errors

• A04 with PV1-2 = I: inconsistent. Inpatient = A01. Outpatient = A04.
• Visit number (PV1-19) reused for the next session: each consultation has its own visit number, otherwise results bleed together.
• Confusing A04 and A05 (Pre-admit): A05 = pre-registers a future admission, A04 = registers a current ambulatory act.
• No durable PID-3 identifier: a local MRN is required to attach subsequent Observations and Encounters.

Related ADT events