HL7 Message Components
An HL7 message consists of one or more segments. Each segment consists of one or more composites, also known as fields. The following article provides a typical sample HL7 message, and describe segments and composites in more detail. Example HL7 Message HL7 messages are in human-readable (ASCII) format, though they may require some effort to […]
HL7 Segments
In an HL7 message, each segment of the message contains one specific category of information, such as patient information or patient visit data. For example, consider the sample HL7 message that you saw in the previous section: In an HL7 message, the name of each segment in the message is specified by the first field […]
HL7 Composites
Each segment of an HL7 message consists of one or more composites (also known as fields). By default, the | (pipe) character is used to separate one composite from another. A composite can be a primitive data type (such as a character string or a number), or can contain other composites. If a composite contains […]
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 […]
