Friday, March 31, 2017

The Longitudinal Identity of a CCD

This question comes up from time to time. For a given patient, how is there a unique identifier which uniquely identifies the CCD for the patient as it evolves over time.

The answer is no, but to understand that, we need to talk a little bit about identifiers in CDA and how they were intended to be used.

Every CDA released into the wild has ONE and only ONE unique identifier by which it is uniquely known to the world.  That is found in /ClinicalDocument/id.  During the production of a clinical document, there are some workflow cases where the document has to be amended or corrected.  And so there is a need to identify a "sequence" of clinical documents, and possibly even to assign that sequence an identifier.  The CDA standard supports this, and you can find that in /ClinicalDocument/setId.

BUT... that field need not be used at all.  You can also track backwards through time using /ClinicalDocument/relatedDocument/parentDocument/id to see what previous version was revised.  And the standard requires neither of these fields to be used in any workflow.

So ... couldn't I just use setId to track the CCD for each patient?

Yes, but fundamentially, you'd be doing something that fails to take into account one of the properties of a ClinicalDocument, and that is context.  Context is the who/where/what/when metadata associated with the activity that the clinical document is reporting on.  When setId is the same for two clinical documents, the assumption is that the Context associated with the content is the same, OR, is being corrected, not that it is being changed wholesale.

The episode of care being reported in a CCD is part of its context, as is the when the information was reported.  If you want to report on a different episode of care, it's not just a new document, it's also a new context.  And that's why I suggest that setId should be different.

This is mostly a philosphical debate, rather than one related to what the standard says, but when you think about the history of clinical documents, you might agree that it makes sense.

Clinical Documents aren't "living" documents.  A key definition of a CCD document is a summary of relevant and pertinent data "at a point in time."  It's that "point in time" part of the definition that makes the CCD document a static item.


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