In the previous article, we talked about the flow of data to request the test and receive the results of the requested test. Now let's talk about one of the most important messages of HL7v2 standard.
Every time a receiving application accepts a message and consumes the message data, it is expected to send an ACKnowledgement (ACK) message back to the sending application. The sending application is expected to keep on sending a message until it has received an ACK message. It is done to inform the sending application that its message was successfully received, that it is (not) valid in accordance with HL7 rules and, if it is compliant, that it will be processed at some point.