CCD and HL7 V3 / V2

Question

My company is going to be an HIE and we are figuring out how to exchange our information with other systems. We are located in USA and I see that the current common standard is HL7 V2. Hl7 V3 is not backward compatible to HL7 V2. These are the transactions that we are planning to implement:
o Discharge Summaries
o Progress Notes
o Lab Results
o Procedures/Orders

This whole thing is complicated and I am trying to figure out using bits and pieces of info scattered in the net. So here are my questions:

1. Should we look at HL7 V3 or V2 implementation?
2. Are CCD and HL7 V2 compatible? Most of the documents I saw from HITSP talks about HL7 V3.
3. Where can I find an exhaustive list of data fields which are required for all the transactions above? Is it defined by HITSP?
4. Do the fields defined for each transaction change depending on whether we go with HL7 V3 or V2?

Any help will be much appreciated!

Answer 1

If you're going to be an HIE, you're going to need to handle both HL7 v2 and v3. My experience is that almost all "real life" data transmission is v2 (I think this is probably because most systems capable of v3 transmission also allow v2 formatting, whereas the older systems cannot handle v3, but this is just speculation). There's a very superficial overview of the core differences between v2 and v3 here, which talks a bit about what fundamental changes are being made besides format (delimited vs xml)

The second part of your questions doesn't really have a definitive answer, and ties in with your fourth question. CCD can be HL7v2 compatible, but it's a lot more difficult and relies on the sender and receiver both having a common understanding on a number of issues (hl7v2 is a very loose "standard"). Here's HL7standard.com's thoughts on the subject:

The short answer is "yes" with the long answer being "it depends."

There are different levels of CDA/CCD documents. It probably would be possible to create a Level-1 CDA document from an HL7 v2 message, assuming you had a fairly robust HL7 v2 report of some flavor (MDM or ORU type of message most likely).

It would be harder to take an HL7 v2 message and convert it into a Level-2 or Level-3 CDA document. More data is required in those formats, and that data needs to be structured, not just free form text.

The CDA is based on the HL7 v3 RIM, and compliant CDA documents will follow that data model. Mapping from one data model to another can be challenging.

All CDA documents need to have a responsible party or person who 'signs' the document. At a minimum, the HL7 v2 message would have to have this information.

Converting a CDA document into an HL7 v2 message is possible, but you run the risk of losing the 'context' of the data that is in the original document if it is a highly structured Level-2 or Level-3 document. If the CDA contains nothing more than a textual report and some patient demographic information, then it can be converted into a comparable v2 message.

For getting a full list of fields, I'd just purchase the full HL7 standard... and maybe have a look over at bluebuttonplus.org... though keep in mind that v2 can result in some confusion, as message sub-segments aren't always consistently used between different actors. Anyway, I don't think that there are clean answers to most of what you're asking, but at the very least you will really need to handle both formats. I'd also throw in that you may want to look at a product like Mirth or InterfaceWare to handle some of your parsing and testing.