The Health Level Seven (HL7) Messaging Standard Version 2.2 and higher was recommended to the Secretary of Health and Human Services by the NCVHS as the messaging format standards for the PMRI.2 HL7 is a not-for-profit volunteer standards development organization that brings together developers, users, and vendors of electronic health record systems to develop standards that enable the exchange, or interoperability, of data and information across health care applications (www.hl7.org).
HL7 messaging standards specify the technical aspects of sending messages so that one software program can exchange information with another and have that information "understood" by the receiving machine. The format of the current version of the standard was developed for order entry, scheduling, medical record/image management, patient administration, observation reporting, financial management, and patient care transactions. An example of an HL7 ADT transaction message follows3:
This message is reporting an observation/result (OBX). Key fields in the message include the value type (string), the observation identifier (93000.1^ventricular rate (EKG)), the observation value (91), the units (beats/minute), and the reference or normal range for this test (60-100). It is important to recognize that HL7 messaging standards only provide for the structure of the message; they do not provide content for that message. The message standard is analogous to an envelope in which one can insert a letter; coded terminologies provide the content of the message.
The HL7 version 3 messaging standard currently under development is of particular interest because, in contrast to specifying the slots into which data and values are inserted as in the example above, version 3 will specify the complex data model (or information model) that carries the meaning or semantics of the data; HL7 version 3 will provide the syntax for messages that enables the vision of the NHII (i.e., make explicit the semantic and lexical connections that exist within the fields of HL7 messages). The terminologies provide the content of those messages. As a result, it will be technically possible to use data that was recorded at the point of care for multiple purposes, e.g., generating required patient assessment reports from clinical documentation systems.