The HL7 2.5 standard defines close to 500 different message types. While some are only used occasionally, almost all HL7 interfaces will incorporate the H7 acknowledgment (ACK) message. An HL7 ACK message is used to insure that HL7 messages are delivered from system to system without being lost.
Like any technology company, occasionally we have our own internal IT problems to deal with. This week it happened to be our mail server. For a period of time, we were not receiving any external e-mail, but we were unaware of the problem until a customer called us to let us know his e-mail had bounced. Once we were aware of the problem, fixing it was trivial. This got me thinking about the way HL7 messages are delivered, and the importance of HL7 acknowledgment messages.
In the clinical world, the successful and timely delivery of HL7 messages is critical. Tens of thousands or even hundreds of thousands of messages are transported daily in a typical hospital environment. When a medical application (HIS, LIS, RIS…) sends an HL7 message, it immediately needs to know that message was delivered successfully. Only once the successful delivery of the message has been verified should the next message in the queue be sent.
HL7 integration engines or HL7 enabled applications need to be able to generate properly formatted HL7 responses for all messages that they receive. Also, with HL7 messaging, applications should be configured to wait to receive an HL7 formatted response prior to sending the next message in their queue.
Most applications will take the ACK qualification a few steps further and verify not only that the message they receive is an HL7 ACK message, but also that the data contained within this message matches the data from the previously sent message and that the status of the ACK is a positive response. This is known as original mode acknowledgement. A vast majority of HL7 interfaces today use original mode acknowledgment.
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