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HL7 ADT Messages

The contents of this whitepaper are published under the Creative Commons Attribution-Share Alike license.
See http://www.ringholm.com/docs/00210_en_HL7_ADT_messages.htm for the latest version of this document.
Author: Ren� Spronk, Sr. consultant, Ringholm.
Document status: Final, version 0.8 (2008-08-21)
Please send questions and comments to rene.spronk@ringholm.com.


HL7 ADT messages (Admission, Discharge and Transfer) are a group of messages as defined in the HL7 version 2.x messaging standard. The focus of ADT messages is to convey data related to patient demographics and/or to healthcare encounters (visits). ADT messages are implemented by almost all software applications in a hospital setting.

1. Introduction

The HL7 version 2 standard has the aim to support hospital internal workflows. Each of the chapters of the HL7 standard covers a different subset of the overall workflow: chapter 3 (ADT) supports workflows that require the exchange of patient demographics and/or encounter information.

Chapter 3 (ADT) defines a number of message structures and trigger events.

2. Trigger Events

A trigger event is the underlying reason for transmitting a message, e.g. �Patient has been admitted to the hospital�, �Patient address has changed�, or �Patient has moved from room 23 to room 29�. As soon as a trigger happens, a message is sent to all systems that have an interest in that particular type of information, enabling the receiving application to synchronize it�s database with the data as known by the sender of the message.

Examples of ADT trigger events (coded A01 up to A62) include:

  • A01: Admit notification � an inpatient encounter has started. The patient has been admitted and has been assigned to a location (room or bed)
  • A02: Transfer notification � a patient has been transferred from one location to another one.
  • A03: Discharge notification � the encounter has ended. The prior location assigned to the patient is made available for use by another patient.
  • A04: Patient registration notification � an outpatient encounter has started.
  • A05: Pre-admit a patient notification - the pre-admission process of a patient has started; registration of a non-admitted patient.
  • A08: Update patient information notification � unspecified details of the encounter or the patient demographics data have changed. This trigger event represents a �other changes� category if a more suitable Axx trigger event doesn�t exist.
  • A11: Cancel admit notification � the start of an inpatient encounter, for which a previous admit notification message was sent, has been cancelled.
  • A12: Cancel transfer notification � the location transfer, for which a previous transfer notification message was sent, has been cancelled.
  • A13: Cancel discharge notification � the end of an inpatient encounter, for which a previous discharge notification message was sent, has been cancelled.
  • A40: Merge patient identifier list notification � two or more patient records, each identified using a different set of patient identifiers, have been merged.
Even though the standard itself doesn�t explicitly define a sequence in which these trigger events occur, it seems clear that normally a patient has to be admitted (A01) before he or she can be transferred (A02) and discharged (A03).

Sequence of HL7 ADT trigger events

3. Message Structure

The message structure may vary depending on the trigger event. A trigger event related to the �transfer of a patient� has a different structure than a �change of a person�s address�, or a �merge two patient records�. The following segments (in HL7 version 2 all messages are comprised of multiple segments) are of core importance in this chapter:

  • PID: Patient ID � contains information which identifies the patient (e.g. name, gender, birth date, patient identifier, national person identifier) as well as patient demographics information (e.g. address, telephone numbers).
  • PV1: Patient Visit � contains information about the encounter (a.k.a. Visit). This segment includes (amongst other things) the type of encounter, its start/end date and time, the admitting and attending physicians.

4. Summary

HL7 ADT messages (Admission, Discharge and Transfer) are implemented by almost all applications used within a hospital setting. The ADT trigger events typically occur in the administrative system of the hospital (Hospital Information System - HIS or Patient Administrative System - PAS). The resulting messages are sent to all ancillary systems enabling them to synchronize their application database with the latest information as available in the main administrative system.

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