HL7 is the abbreviation for the term, Health Level-7. The organization, HL7, provides international standards for the structuring and transmission of clinical and administrative data in the healthcare domain. One HL7 interoperability specification used for many years has been version 2.x, otherwise known as V2. V2 has been a standard used to codify medical (led by billing) information and transmit it between computerized medical systems. The standard was developed and finalized during the 1980s, and thus was optimized for lower memory and storage usage in the very early stages of networked computing; thus it was an implicitly typed flat-file.
While everything in V2 was text-based, it was a grid of information separated by a vertical text character known as a “pipe” (|). In order for a user to read it, he/she had to know the order of the fields and needed different glossaries to sort out the meanings of various codes. It was very thorough, but at the same time, having information in the wrong order or adding extra information could break the meaning of the whole message. It also only allowed for about 20% customization.
Here’s more information, including examples, of HL7 V2. Source: Ringholm Whitepapers: http://ringholm.com/docs/04300_en.htm
After V2, came Version 3 (V3). V3 was an additional standard to V2 developed during the 1990s that focused on customization and incorporation of web-service technologies and the Extensible Markup Language (XML) that came with it. The data was explicitly typed (being defined by an element or attribute title) and could more flexibly be regulated and defined by schemas. There was also more flexibility introduced with extension logic. But while it was easier for humans to read, it involved massive documents and very rigid structures and programs that were designed to work with large document-object-models. Often, a user needed a computer program to interpret the meaning in an easy-to-comprehend format.
Here’s more information, including examples, of HL7 V3. Source: Ringholm Whitepapers: http://ringholm.com/docs/04300_en.htm
Here’s more information, including examples, of CDA. Source: Github Project Examples: https://github.com/brettmarquard/HL7-C-CDA-Task-Force-Examples/blob/master/No_Known_Medication_Allergies_Status_with_Author_Timestamp.xml
Fast Healthcare Interoperability Resources (FHIR) is a very new draft standard for the exchange of resources. FHIR is a set of “best-of” standards and implementation resources from HL7 V2, HL7 V3, and HL7 CDA. FHIR is broken up into resources that can be combined to handle the majority of emerging medical messaging and documentation needs, and each resource has a common way to identify them, common metadata, and a human readable portion.
You can learn more about FHIR at this site: http://hl7.org/implement/standards/fhir/
It is also important to note that HL7 V2, V3, CDA and other released standards can be found in both legacy as well as newly developed IT systems. today and in new systems. HL7 is creating and updating standards to be used as tools in response to an ever changing landscape of needs, but isn’t trying to influence which standards are used for various messaging and documentation functions. Most of the guidance HL7 issues have to do more with data integrity and security using whatever standard developers choose.