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CDA implementation experiences in the UK

Publication date: Dec 04, 2012

The initial joint HL7 UK / DHID CDA Implementation Forum meeting focused on the implementation aspects of CDA, on template and example repositories, and featured a panel discussion on the best approach for the implementation of CDA documents within an application.

On November 4th (2012) HL7 UK held a joint meeting with the DHID CDA Implementation Forum. The CDA Implementation Forum is an initiative (started in August 2012) by the English NHS to share implementation best practices related to its CDA specifications (i.e. those part of the English ITK/MIM specifications).

Note for non-UK readers: the Interoperability Toolkit (ITK) is a HL7 v2, HL7 v3 message and CDA based implementation guide for use at the local/regional level within England. The Message Implementation Manual (MIM) is a HL7 v3 and CDA based implementation guide for use at the national level within England – the development of this specification has been on hold for the past 2 years or so, the focus is currently on the ITK. The Department of Health Information Directorate (DHID, part of the English NHS), and more precisely Connecting for Health (CfH) is responsible for the creation of the ITK and for accrediting compliant systems.

Participants of the joint HL7/DHID CDA Forum meeting

UK CDA Implementation experiences

First we had three presentations from those with CDA implementation experience in the UK . Below are the key points that I got out of the presentations:
  1. Keith Strahan (on behalf of the London health and social care information sharing programme) talks about their Adapter project. Current interoperability scenarios (e.g. Admit and Discharge forms) are based on sending fax. Theirs is a gradual approach: (a) start to use secure e-mail as a transport mechanism, maybe move to the ITK infrastructure afterwards, and (b) use a piece of middleware to map structured (MIM v3 messages) and unstructured documents (word documents) data to/from CDA for those organizations that can use structured data as defined in the ITK CDA profiles. The ITK specification needs updates to deal with the concept of middleware.
  2. Nigel Miller (on behalf of the CLCH project for e-Communication, a London based primary healthcare provider oriented project) discusses a project related to the exchange of data between GPs. They looked at CDA as a potential format. However, CDA isn’t currently supported by GP systems, so they decided to fall back on Kettering XML (a legacy, non governed standard) which works with all GP systems. Need somehow to put pressure on suppliers to achieve ITK compliance. Keith Naylor (DHID/NHS) points out that there is an as of yet unsigned directive that GP systems at some point in the future will have to provide (at zero cost) support for the receipt of CDA.
  3. Dunmail Hodkinson (Black Pear Software) discusses a project that focuses on the implementation of an ophthalmology system based on iPads, and to link the outreach clinics that use these with hospital systems, particularly the OpenEyes application (an open source ophthalmology system). For example glaucoma findings (CfH already had a well-defined Glaucoma dataset, also inclusive of the IHE Eye Care profile). The clinical model is based on CKM (the OpenEHR Clinical Knowledge management tool). They ended up using the attachment feature in a CDA entry to convey the OpenEHR XML (mime type application/openehr+xml), in addition to a human readable text version in the section. This (in due time) allows for a migration of the openEHR XML content to CDA entries. They used the CDA API (an open source API for the ITK non-structured CDA specification) to create CDA quickly. Their conclusion: it’s a lot work to create CDA interfaces. Typically for a small projects: an ad hoc interface takes a week, this took 2 to 3 months.

Template management

Richard Kavanagh (head of data standards, NHS CfH) presented the new CfH Template Library. The CfH approach towards templating was developed years ago, much ahead of any other international project, now enshrined in our legacy. There are currently about 280 templates (available on TRUD - requires a login), a next release with instance examples is expected in February 2013) of various types and status. CfH is now moving to template definitions that are specific to the underlying serialized XML - effectively the template is no longer a model constraint but an XML constraint. Provide ability for local projects or vendors to define new CDA profiles (using a “CDA Profile builder”) based on a pick-n-mix selection of assured templates from the Template library.

During the subsequent panel discussion two main topics were discussed:

  • Template versioning (because of the iterative process of defining them), and
  • the different methods of implementing CDA (Example based, model/code generation based, green CDA) and what would be suitable for a particular project. I argued the case for model based implementation (see j.mp/gDwZKm), it being the only method that scales well – especially for vendors that have to deal with templates from lots of sources, and not just the CfH specifications. Dunmail pointed out that as a vendor he doesn’t want to focus on things like schema and schematron, so any generated code that has been made available would make life a lot easier for him.

Robert Worden (Open Mapping Software), talks about (the proof of concept) of a CDA Examples Repository, with multiple examples for each template. Examples are sourced from example CDA documents. It is also a discussion forum (on a template level, or on an XML node level), and a validation service (checks for XML elements that are populated in this instance, but in no other known example, and a crude CDA/template validation).

From right: Dunmail Hodkinson, Ann Wrightson and other participants.


It is apparent from the discussions and the experiences of CfH with the CDA Forum (the online ITK CDA implementer community) that it’s still early days for implementers: most of them are still facing the steep learning curve.

Implementers on the CDA Forum currently don’t raise a lot of issues or implementation approaches on their own. Given that the number of well experienced implementers is low some of the implementers may choose not to discuss experiences because of competitive reasons. Newbies probably wish not to be (publicly) seen as being ignorant. Once there is a certain critical mass of experienced CDA implementers the CDA Forum probably will find much more active participation than it currently does. HL7 UK may be involved in organizing a hack-a-thon which is likely to bring yet more implementers to the table. It may be the right incentive for both newbies as well as experienced implementers to show up, to informally test and develop against the ITK CDA specifications.

The need for examples was raised at various points during the day – which isn’t just beneficial for newbie CDA implementers but also to those that want to test their own implementation. As such Robert Worden’s CDA Examples Repository really fills a need – provided HL7 UK can somehow convince the various implementers to share their own examples/test documents. As part of the next steps Ann Wrightson (TSC chair, HL7 UK) suggests that HL7 UK and the DHID CDA Forum have future joint meetings (this one had a good mixture of regular HL7 UK attendees and CDA Forum participants), whether those be face to face or in the form of a series of webinars. Given that we need to increase the number of CDA implementations to reach the necessary critical mass to get the implementer community going it seems we (as a community) have to do a lot of education and marketing.

I’m personally convinced we’re close to the tipping point – the ever increasing interest in purchasing ITK enabled applications on the supplier side will ensure a higher uptake of CDA over time.


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