HL7 Resources

HL7 Messages

HL7 messages transmit data between disparate systems. An HL7 message consists of a group of segments in a defined sequence, with these segments or groups of segments being optional, required, and/or repeatable (referred to as HL7 cardinality).

The HL7 message type defines the purpose for the message being sent and is present in every HL7 message. Message types are identified by a three-character code, and are used in conjunction with a trigger event. An HL7 trigger event is a real-world event that initiates communication and the sending of a message, and is shown as part of the message type. Both the message type and trigger event are found in the MSH-9 field of the message.

For example, the MSH-9 field might contain the value ADT-A01. This means that ADT is the HL7 message type, and A01 is the trigger event. In the HL7 Standard, an ADT-A01 message is known as a “patient admit” message.

Each message type and trigger event within a specific HL7 version has a defined format. There are some message types and triggers that have the exact same format, such as ADT-A01, ADT-A04, ADT-A05 and ADT-A08. But in many cases, the formats vary widely.

Defining an HL7 Message (examples)

Most commonly used HL7 message types include:

  • ACK – General acknowledgement
  • ADT – Admit, Discharge, Transfer
  • BAR – Add/change billing account
  • DFT – Detailed financial transaction
  • MDM – Medical document management
  • MFN – Master files notification
  • ORM – Order (Pharmacy/treatment)
  • ORU – Observation result (unsolicited)
  • QRY – Query, original mode
  • RAS – Pharmacy/treatment administration
  • RDE – Pharmacy/treatment encoded order
  • RGV – Pharmacy/treatment give
  • SIU – Scheduling information unsolicited

For a full list of all HL7 message types, refer to Appendix A of the HL7 V2 Standard.

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