HL7 MSH – Message Header
The HL7 MSH (Message Header) segment is present in every HL7 message type and defines the message’s source, purpose, destination, and certain syntax specifics like delimiters (separator characters) and character sets. It is always the first segment in the HL7 message, with the only exception being HL7 batch messages.
There are 19 fields in the MSH segment, six of which (field separator, encoding characters, message type, message control ID, processing ID, and version ID) are required for all messages processed using the HL7 standard. The most important of the MSH fields, and perhaps the most important field in the entire message, is the MSH-9 (Message Type) field. This field specifies what type of message is being transmitted (ADT, ORM, ORU, ACK, etc.) and what the trigger event is. When a message is loaded, often the first field examined in order to determine processing is the value in this field.
Based on the following helpful link:
The fields in the MSH segment are as follows:
|7||26||TS||O||Date/Time of Message|
|10||20||ST||R||Message Control Id|
|15||2||ID||O||Accept Acknowledgement Type|
|16||2||ID||O||Application Acknowledgement Type|
|19||3||CE||O||Principal Language of Message|