Version 2 (V2) of the HL7 standard is now used in over 90% of American hospitals and in many other countries including Canada, Australia, Germany, the Netherlands and Japan. HL7 V2 has a broad scope covering patient administration (admission, discharge, transfer and registration), accounting systems and clinical data, such as laboratory orders and reports.

  • The structure of Version 2 messages is modelled on that of ANSI X.12 and UN/EDIFACT.
  • Each information exchange is initiated by a trigger event and consists of one or more messages.
  • Each message is a sequence of segments in a defined sequence. The first segment of each message defines the message type and the type of trigger event that caused the message to be sent. Segments may be mandatory or optional, and may be allowed to repeat.
  • Each segment is a sequence of data fields, separated by special data field separators (usually the pipe ‘|’ symbol). Each segment has a unique 3-character code name. Each segment is terminated by a ‘carriage return’ field. Data elements to the right of this are omitted from the message. Any empty fields to the left are indicated by consecutive data field separators (‘||’).
  • Each data field has a data type, which may be compound ­ made up of components which are separated by a component separator (usually the carat ‘^’ symbol).
  • HL7 Version 2 has evolved over the years. Versions 2.0, 2.1, 2.2, 2.3, 2.3.1, 2.4, 2.5, 2.5.1, 2.6,2.7 and 2.7.1 were published between 1988 and 2011.
  • The Version 2 series is backward compatible.
  • For a diagram explaining how version 2.x fits in with version 3 click here.

To understand the differences between versions you may like to visit the Ringholm website where these are highlighted by René Spronk, Ringholm bv.

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