By convention, a standard segment grammar notation is defined to provide a convenient way to indicate the segments that can be included in a particular type of HL7 message. Many vendors use this segment grammar notation to specify what segments may be included with each type of HL7 message that they send.
In the standard segment grammar notation, segments are listed from left to right, starting with the first segment in the message (which is always MSH). For example, consider this HL7 message, which you have seen before:
MSH|^~\&|EPIC|EPICADT|SMS|SMSADT|199912271408|CHARRIS|ADT^A04|1817457|D|2.5|
PID||0493575^^^2^ID 1|454721||DOE^JOHN^^^^|DOE^JOHN^^^^|19480203|M||B|254 MYSTREET AVE^^MYTOWN^OH^44123^USA||(216)123-4567|||M|NON|400003403~1129086|
NK1||ROE^MARIE^^^^|SPO||(216)123-4567||EC|||||||||||||||||||||||||||
PV1||O|168 ~219~C~PMA^^^^^^^^^||||277^ALLEN MYLASTNAME^BONNIE^^^^|||||||||| ||2688684|||||||||||||||||||||||||199912271408||||||002376853
The segment grammar notation for this message would be:
MSH PID NK1 PV1
In the segment grammar notation, optional segments are enclosed in square brackets []. For example, if a PV2 (Patient Visit - Additional Information) segment can be optionally included with messages such as the one shown above, the segment grammar looks like this:
MSH PID NK1 PV1 [PV2]
Repeating segments are enclosed in curly brackets {}. For example, if multiple NK1 segments can be included, the segment grammar looks like this:
MSH PID {NK1} PV1 [PV2]
A segment that is both optional and can be repeated is enclosed in both square brackets and curly brackets. For example, if the NK1 segment is optional but can be repeated, the segment grammar looks like this:
MSH PID [{NK1}] PV1 [PV2]
Optional or repeating segment groups are indicated by specifying multiple segment names inside square brackets or curly brackets. For example, consider the sample Lab Result message that you have seen earlier:
MSH|^~\&|MESA_RPT_MGR|EAST_RADIOLOGY|REPOSITORY|XYZ|||ORU^R01|MESA3b781ae8|P|2.5||||||||
PID|||CR3^^^ADT1||CRTHREE^PAUL|||||||||||||PatientAcct||||||||||||
OBR||||4550|||20010501141500.0000||||||||||||||||||F||||||||||||||||||
OBX|1|HD|SR Instance UID||1.113654.1.2001.30.2.1||||||F||||||
OBX|2|TX|SR Text||Lungs expanded and clear. Conclusions Normal PA chest x-ray.||||||F||||||
OBR||||4551|||20010501141500||||||||||||||||||F||||||||||||||||||
OBX|1|HD|SR Instance UID||1.113654.1.2001.10.2.1.603||||||F||||||
OBX|2|HD|Study Instance UID|1|1.113654.1.2001.10||||||F||||||
OBX|3|HD|Series Instance UID|1|1.113654.1.2001.10.1||||||F||||||
This message can optionally contain one or more Result Groups, with each Result Group consisting of one OBR message and one or more OBX messages. The segment grammar notation for this message is:
MSH PID [{OBR {OBX}}]
Here, OBR {OBX} is the segment grammar notation for a Result Group. The Result Group is enclosed in both square and curly brackets, as it is optional and can be repeated.
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