HL7 Delimiter Characters
As you have seen in the previous sections, certain special characters separate one composite in a segment from another, or separate one sub-composite from another. These special characters are known as delimiter characters. This section describes delimiter characters in more detail, how to use escape characters to include a delimiter character as part of a […]
Delimiter Escape Sequences
If an HL7 message contains one of the special delimiter characters as part of its message content, you can use a special escape sequence to specify the delimiter character. This ensures that any application that processes HL7 messages can always distinguish between a delimiter character and a character that is part of the message text. […]
HL7 Delimiter Redefinitions
The HL7 Delimiter Characters section lists the default delimiter characters that are normally used in HL7 messages. An HL7 message can choose to employ HL7 delimiter redefinitions in order to use different delimiter characters if the standard characters are not convenient to use. In any HL7 message, the delimiter characters that the message is using […]
Determining the HL7 Message Type
Each HL7 message is of a particular message type. This HL7 message type indicates what health-related information is being provided in this message. The message type also determines what segments can be included as part of the message. To determine the message type of an HL7 message, examine its MSH segment. The message type is […]
Repeating and Optional Segments
Some HL7 message types allow a segment to be repeated one or more times, or allow a segment to be optionally present. For example, repeating segments are useful for messages that contain contact information, as they make it possible to provide more than one contact. For instance, multiple NK1 (Next of Kin) segments may be […]
Custom Segments: HL7 Z-segments
If an HL7 message contains customized data that cannot be included in any segment that is defined for its message type, you can create a custom segment to transmit this data. By convention, all custom segments begin with the letter Z. For example, a ZPD segment could be created to contain customized patient demographics information. […]
Present but Null Fields
In segments, it is important to note that there is a difference between fields that have no value defined for them and fields that have a null value defined for them. If a field is not defined, there is nothing between the two | characters that delimit the field: OBR||||||||| A null value is indicated […]
HL7 Segment Groups
Some message types support segment groups. A segment group is a collection of segments that always appear together. Some segment groups can be optional or repeating. For example, messages of type ORU^R01 (Lab Result) can have one or more Result Group segment groups defined. Each Result Group consists of one OBR (Observation Request) segment and […]
HL7 Segment Grammar Notation
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 […]
HL7 Versions
To make it easier to send and receive health-care information, the HL7 organization has defined a standard that specifies what types of HL7 messages can be sent, what segments can be included in these messages, and what fields can be included in their segments. The HL7 standard is constantly evolving. To date, the HL7 committee […]
