ACK (Acknowledgement)

In HL7, an ACK is the message sent from a receiving system to a sending system, signalling that data has been received successfully.

HL7 provides different codes that can be included with ACKs to state whether the data was:

  • Received (AA),
  • Received and processed (CA),
  • Contained errors (AE), or
  • Was outright rejected (AR).

ACKs with error codes are often referred to as NAKs or NACKs (negative-acknowledgements) though it’s not actually a different message type.