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Step 3

Message types

ADT, ORU, ORM. How the MSH-9 field decides everything else.

Every HL7 message looks alike at first glance. Yet an admission, an order and a result have nothing in common. What tells them apart sits in a single field: MSH-9, the message type. Learn to read it, and you instantly know what you are dealing with.

MSH-9 reads in two pieces

The MSH-9 field has the form CODE^EVENT. The first piece is the messagefamily, the second is the trigger event, the specific situation. For example ADT^A01: family ADT (patient movements), event A01 (admission).

Switch messages below and watch MSH-9 change. Click it to see it explained in plain words.

A sleep study report. The lab sends the hospital record an AHI of 28.5/h, flagged “high”: severe sleep apnea.

ORU^R01· Observation result (unsolicited)
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The main families to know

  • ADT (Admission, Discharge, Transfer): every patient movement.A01 admit, A02 transfer, A03 discharge,A04 register, A08 update.
  • ORM / OMG: an order. You request a test, a drug, a procedure. This is the message that triggers something.
  • ORU (Observation Result): a result coming back. A lab report, a polysomnography. R01 is the usual event.
  • MDM: a medical document. SIU: an appointment.ACK: the acknowledgement a system sends back to say "received".

Same family, different events

The strength of the system: a family shares the same structure, and the event pins down the situation. ADT^A01 (admit) and ADT^A03 (discharge) read the same way, they just tell two different moments of the patient's journey. Learn one family, handle all its events.