Looking back over the past year, I’ve given a number of talks on FHIR. I’ve also been lucky enough to have been sponsored by my employer – Orion Health – to speak at a number of overseas conferences, including CHIMA in China, and HIMSS Asia-Pac in Hong Kong.
In most of these presentations I’ve started by giving an overview of the HL7 Interoperability standards, and where FHIR fits into that family, including why it was developed in the first place. Sounds like a good topic for a blog post!
The first version of HL7 (which was actually version 2) was developed around 1987 by Ed Hammond in response to a need to share health information within a healthcare enterprise. The name “HL7” stands for ‘Health Level 7’ – where the 7 refers to the 7th layer (applications) of the OSI model.
I asked Ed why the version was 2 and not 1 – he replied that there was a initially a version .5 that was more of a scoping version, and a version 1.0 that was demonstrated at a HIMSS conference. This was more what we would call a DSTU (Draft Standard for Trial Use) today. Version 2.0 was the first version that made it “into the wild”.
The standard become widely used – largely due to it’s relative simplicity, but also because it allowed individual implementers to define ‘extensions’ to the standards in the form of ‘Z-segments’ which allowed them to share data that had not yet been formally defined in the main HL7 standard.
However a number of issues developed over the years.
- Implementers produced a proliferation of overlapping Z-segments that could only be understood by the the parties that defined them – usually a single sender and recipient.
- People started using the defined fields within segments for unexpected purposes – for example if their particular implementation did not need to use a particular field for the defined purpose, they ‘re-used’ it for something else.
- Individual segments got more and more fields added – with any of them optional
This led to the saying the ‘Once you’ve seen one HL7 v2 implementation – you’ve seen one HL7 v2 implementation!’ Semantic interoperability – being able to communicate ‘meaning’ was really restricted to individual sets of trading partners who would agree in advance what the meaning of these ‘extended’ fields was.
In response to these issues, HL7 started work on version 3 around 1995. Version 3 created a common ‘Reference Information Model’ and a standardized development process, from which the various HL7 artefacts were derived. It was an ambitious programme (and not without critics) as it attempted to provide a mechanism to share any clinical information without necessarily having to agree in advance what that information was. The first release was in 2005.
However, with the exception of CDA (Clinical Document Architecture), version 3 didn’t really take off. It was used in Canada (Health Infoway) and the UK (Connecting for health), but most people continued to use v2 for messaging needs, and CDA for documents (in fact – people started using CDA where a messaging approach was really required – as a document standard, CDA does not support workflow). There were a number of reasons for this.
- Using v3 properly is hard. It is a very abstract standard, and you need to understand quite a bit about it to work with and extend the standard.
- Development of new business ‘domains’ was slow – 3-7 years to become ‘normative’ was not unusual.
- All of the tooling to develop and publish standards needed to be custom built.
- It has been said that v3 is designed to suit the needs of the modeller, not the implementer. For example, with the exception of CDA, there is no standardized XML schema across all v3 messages.
- In most cases v2 continued to do the job – why change?
- The world had moved on – real-time connectivity and the standards that support that (HTTP, XML, JSON, REST, ATOM and many others) were commonplace, as was the concept of “API’s” to support the electronic exchange of information.
Recognizing these issues, the HL7 Board commissioned a ‘fresh look’ at HL7 in 2011. The mandate was ‘What would we do if we were starting with healthcare interoperability from scratch today’? The team noted that:
- HL7 doesn’t really have a ‘modern’ standard for, say, mobile application or cloud developers.
- There was a lot of good work and thinking in v3 – it was just hard to get at it.
- V2 remains enormously popular, yet is based on old technology (but it is simple to understand, and does support extensibility). A migration path is needed.
- CDA is popular because it supports implementers:
- There is a standard XML schema – that common tools can manipulate
- It supports ‘incremental semantic interoperability’ through human readible text elements
- There is a concise specification, a number of well defined Implementation guides with reference implementations and schematron validators
- There were many implementations of CDA (and CCD – which is a type of CDA) internationally, and a body of knowledge that built up around it.
- You don’t need to understand v3 to use it!
- but – it does not support workflow, and it is designed for the Document paradigm.
Grahame Grieve (from Australia) had already been talking about a different approach – Resources For Healthcare – on his blog (health Intersections) and this was used as the basis to develop what was to become FHIR (Fast Health Interoperability Resources). It was presented at the May Working Group meeting in Vancouver, and quite literally was the star of the show. FHIR had arrived!