Health Level 7
Health Level 7 (HL7) refers both to a family of technical specifications for the exchange of medical information, and to a standards development organization accredited by the American National Standards Institute (ANSI). ANSI is accredited, in turn, to the International Organization for Standardization (ISO). Specifications deal with both transactional and patient record information.
The first HL7 standard, Context Management Architecture (CMA), was approved in 1999. This architecture has continued to evolve, specified representation of a number of clinical data elements, which could then be assembled into meaningful transactions, or documents for such things as medical order entry system/electronic provider order entry (EPOE), test requests and reports, admission and discharge, registration of a new patient, etc. Version 2.5 of this messaging standard, adopted in 2003, has been widely implemented in clinical information systems. The problem of electronic healthcare is less that applications do not exist, and more that they are not installed, used seriously, or interconnected.
In 2000, the Clinical Document Architecture (CDA), formerly known as the Patient Record Architecture, for exchanging such documents, providing an "exchange model" for more narrative information, such as progress notes and surgical reports, which are needed in an electronic medical record (EMR).
Technology
HL7 messaging formats used an HL-7 specific structure, not ASN.1, XDR, or other self-defining structure. The Version 3 specifications, however, assume the use of XML, and there is a supplementary specification for exchanging Version 2.3.1 onwards via XML.
Version 3 also formalizes the software architecture into a distinct object-oriented model, and provides testing methodology.
Interoperability and standards
HL7 messages are compatible with all appropriate information transfer methods in the Internet Protocol Suite. Specific types of information follow domain-specific standards, such as digital imaging and communications in medicine for all types of images, from digital photography to magnetic resonance imaging (MRI),