A short introduction to HL7

HL7 (Health Level Seven) is an international healthcare standard used for the integration of medical systems and the exchange of health integration.  HL7 has been developed in order to reduce the cost of interfacing medical systems.


This standard is developed by a volunteer-based non-profit organization. From 1993 national HL7 organization have existed in addition to the global HL7 organization (HL7 Inc.).


It was founded in 1987 and became an ANSI (American National Standards Institute) accredited standard in 1994.
The name HL7 refers to the seventh layer (application layer) of the ISO OSI reference model.

Version 1.0 was published in 1987 and only supported admission-discharge-transfer, order-entry and display-oriented queries.
Version 2.0 was published in 1988. The backward compatible revisions 2.1 to 2.6 were developed between 1988 and 2007.

Version 2.x is currently supported by all major medical information systems vendors.

In 1995, work was started on HL7 version 3. An initial standard publication in 2005 was published in 2005. HL7 version 3 is based on object oriented principles and on a Reference Information Model (RIM) used to express the data contents.

Although being able to provide a more exact and more powerful definition of the contents of messages, HL7 v3 adoption has been much slower than expected. A few reasons for that are:

  • Most vendors already use an HL7 v2 interface to communicate with other systems so you cannot only have a v3 interface but always also need a v2 interface in order to interoperate.
  • It’s much easier to write a basic v2 interface than using v3 which introduces considerable new conceptual complexity.

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