HL7 Table HL70003: Event Type Code

HL7 v2 table 0003 is the master enumeration of ADT (Admit-Discharge-Transfer) trigger events. Every ADT^A0n message in a hospital interface — the lifeblood of patient registration, bed management, and downstream census feeds — carries one of these codes in both MSH-9.2 Trigger Event and EVN-1 Event Type Code. The table is HL7-defined, OID 2.16.840.1.113883.18.4, published under the canonical URI http://terminology.hl7.org/CodeSystem/v2-0003.

Purpose

Table 0003 answers the question "what just happened to this patient?" in a way that downstream systems can route on without parsing the rest of the message. An EHR fires A01 when a patient is admitted, A02 when they move beds, A03 when they go home, A08 to update demographics. A lab system listening for census changes can subscribe to A01/A03/A08 and ignore the rest; a bed-management dashboard cares about A02/A14/A15 and nothing else.

Because the trigger event drives subscription and routing, table 0003 is one of the few HL7 vocabularies where exact-string matching matters more than semantic equivalence. An interface engine that re-emits an A04 (Register) as A01 (Admit) will break downstream billing logic, because A04 is an outpatient register that does not start an inpatient stay.

Where it's used

The EVN-1 / MSH-9.2 redundancy is a v2.2 holdover. EVN-1 was officially deprecated in v2.3 in favor of MSH-9.2, but virtually every production sender still emits both, and many receivers still validate that they match.

Code list

The full table contains 80+ codes. The primary ADT triggers below cover the vast majority of production traffic; additional codes exist for application-level events (A60 allergy update, Z-events for site-specific extensions) and for the rarely-used "tracking" subset.

Note: additional event codes (A63+, Z-events) exist for site-specific extensions and newer functions; consult the v2.8.1 base standard chapter 3 for the complete list.

Code system OID and canonical URI

• OID: 2.16.840.1.113883.18.4
• Canonical URI: http://terminology.hl7.org/CodeSystem/v2-0003
• FHIR ValueSet: http://terminology.hl7.org/ValueSet/v2-0003

HL7-defined vs user-defined

Table 0003 is HL7-defined — extension is not permitted in conformant interfaces. Sites that need a custom trigger event must use Z-events (Z01, Z02 …) carried in a separate, site-negotiated namespace; they are not valid 0003 codes.

Version differences

• v2.2: Original A01–A20 set defined.
• v2.3: EVN-1 deprecated in favor of MSH-9.2. A18 marked for replacement.
• v2.3.1: A18 (Merge) split into A34/A35/A36 for precise merge semantics; A24 (Link) added.
• v2.5: A39–A45 added for external/internal ID merges and moves.
• v2.6: A46–A55 added for ID change events and attending doctor changes.
• v2.7: A60–A62 added for allergy updates and consulting doctor changes.
• v2.8.1: No new codes; existing definitions stable.

Common mistakes

1. Treating A04 as A01. A04 (Register) creates a person/account but does not open an inpatient stay. Downstream billing systems will reject an A04 routed as an admit.
2. Sending A08 for every update. A08 is a general "patient information changed" event; using it to communicate transfers (which should be A02) breaks bed-management feeds.
3. Mismatching MSH-9.2 and EVN-1. Many receivers validate equality; a mismatch causes ACK rejection.
4. Using A18 in v2.5+. A18 was replaced by A34/A35/A36 in v2.3.1. Modern receivers may not recognise A18 at all.
5. Emitting A11 without the original A01's correlation data. A11 (Cancel admit) requires enough identifiers to undo the A01 in the receiver — missing PID-18 (Account Number) is the most common cause of failed cancels.

Examples

Sample MSH and EVN

MSH|^~&|EPIC|HOSP|LAB|LAB|20260625103000||ADT^A01^ADT_A01|MSG00001|P|2.8.1
EVN|A01|20260625103000|||1234^DOCTOR^WELBY^^^^MD

FHIR Coding JSON

{
  "system": "http://terminology.hl7.org/CodeSystem/v2-0003",
  "code": "A01",
  "display": "Admit/visit notification"
}

Mapping failure

A sender emits MSH-9 = ADT^A04 (Register) for an ED arrival, but the downstream bed-management system only subscribes to A01. The patient never appears on the ED census board until an A06 (Change outpatient to inpatient) fires hours later. Root cause: registration vs admission semantics confused at the sender.

FHIR mapping

There is no direct FHIR ValueSet equivalent to table 0003 — FHIR models the state of an Encounter, not the event that changed it. The v2-to-FHIR IG ConceptMap maps each trigger to an Encounter.status transition:

Engine considerations

• Mirth / NextGen Connect: routing-by-trigger is implemented in the Source Filter using msg['MSH']['MSH.9']['MSH.9.2'].toString(). Avoid filtering on EVN-1 alone — some senders omit EVN entirely.
• Rhapsody / Lyniate: the message-type property exposed in the filter expression already concatenates MSH-9.1^9.2; match against ADT^A01, not A01 alone.
• Cloverleaf: the trigger event is bound to the $msgtype variable; sites typically branch on it in a TPS proc.
• HAPI v2: Terser.get(msg, "/MSH-9-2") returns the trigger event; Terser.get(msg, "/EVN-1") returns the EVN-1 copy.

How Vorro handles

The Vorro engine treats MSH-9.2 as the authoritative trigger and EVN-1 as advisory. Routes filter on the canonical trigger code, and the policy library ships preset rules for the four highest-volume events (A01/A02/A03/A08). When EVN-1 disagrees with MSH-9.2, Vorro emits a non-fatal warning and prefers MSH-9.2 — matching the v2.3+ deprecation guidance. Z-events are passed through unchanged but excluded from the standard 0003 ValueSet validation.

Related pages

• HL7 MSH Segment — Message Header carrying MSH-9.
• HL7 EVN Segment — Event Type segment carrying EVN-1.
• HL7 Table 0004: Patient Class — companion ADT vocabulary on PV1-2.

Sources

• HL7 Terminology — CodeSystem v2-0003
• HL7 v2-to-FHIR IG — ConceptMap table-hl70003 to Encounter.status
• HL7 v2.8.1 base standard, chapter 3 (Patient Administration)