HL7 v2 message types

A message type defines the type of a HL7 v2 message.

What a message type is

Here is a short admission message. The ninth field of the first line is MSH-9, and it holds ADT^A01^ADT_A01.

• ADTThe message type. It says what kind of message this is. ADT covers admissions, discharges and transfers.
• A01The trigger event. It says what happened in the real world. A01 is a patient being admitted.
• ADT_A01The message structure. It says which segments the message carries and in what order.

One structure often serves several events. For example, an A04 registration and an A08 update both arrive as ADT_A01.

Common message types

The standard defines 123 message types. Each page says what the type is for, lists its trigger events and draws each structure as a tree of segments. These are some of the common message types:

• ADTAdmit, Discharge, Transfer

  ADT carries patient administration events: a patient arriving, moving between wards, being discharged, or having their demographics corrected. It is the busiest interface in most hospitals, because almost every other system needs to know who the patient is and where they are.

• ORUObservation Result, Unsolicited

  ORU delivers results without being queried: a laboratory sending back a completed panel, a device reporting a reading, a radiology system releasing a report.

• ORMOrder Message

  ORM message is used to place, change and cancel orders.

• SIUScheduling Information Unsolicited

  SIU reports what has happened to an appointment: booked, rescheduled, cancelled, or the patient failed to attend. Each of those is a separate trigger event on the same message type.

• MDMMedical Document Management

  MDM moves clinical documents and their status: a dictated note becoming available, a transcription being edited, a document being replaced. The document itself travels in OBX segments beneath a TXA header.

• DFTDetailed Financial Transaction

  DFT posts charges and financial transactions against a patient account: a procedure performed, a supply used, an adjustment made. The transactions themselves are FT1 segments.

• ACKGeneral Acknowledgment

  ACK is the reply that says a message arrived and what happened to it. MSA-1 carries the acknowledgment code and MSA-2 echoes the control ID of the message being answered.

All message types

Here's a list of all 123 message types, along with the number of structures and trigger events each one has.