Question: What are the rules around use of SUBJ relationship in CDA?
Apr 3, 2012In the following example from CCD there is an EntryRelationship has a type code of “SUBJ” However the CDA spec says the following which is only valid for OBS to OBS. From the payers section (entry level template): ````
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The restriction from the CDA spec is (section 4.3.8.4):
|SUBJ (has subject)|[Observation | RegionOfInterest] SUBJ [Observation | ObservationMedia]|Used to relate a source region of interest to a target image, or to relate an observation to its subject observation (for instance, source “moderate severity” has subject target “chest pain”).The ActRelationshipType “has subject” is similar to the ParticipationType “subject”.Entries that primarily operate on physical subjects use the Participation, whereas entries that primarily operate on other entries use the ActRelationship.
Note the all important text at the top of that table, however:
**NOTE: **The CDA specification permits any CDA entry to relate to any CDA entry using any of the following relationship types. In many cases, this would result in nonsensical relationships. The following table is a guideline for reasonable relationships between CDA entries, and is not a conformance constraint.
So that’s just a guideline. A lot of implementers get caught out by that. Because of the shortness of the allowed list of act relationships, SUBJ and COMP are (ab)used quite a lot. This CCD usage is common.
Further SUBJ seems to be a strange choice of ER type code To me at least) it would seem to be more like a COMP. What is the purpose of having the procedure nested within an Entity Relationship. I cannot see what you gain over having the PROC ER directly under the . policy activity.
No, indeed, not in this case. However the key answer is here (from CCD spec):
NOTE: To the extent possible, the conformance statements in this section are isomorphic and compatible with the HL7 Financial Management (FM) domain model. In some cases, CDA R2 lacks class codes or other RIM components used by FM, in which case the closest corresponding CDA R2 representation is used.
The reasoning is not evident either in the CCD examples or the specification, but the full blown model (the claims and billing domain model) contains a richer model where the introduction of the intermediate act makes sense (aligns with a policy statement act, and the procedure is extra to the DMIM).
More generally, SUBJ is used where the extra information is “about” the act, whereas COMP is used when the extra information is “part” of the act. Sometimes, that’s a sensible differentiation, but often, from the perspective of the use case, it’s an arbitrary decision which to use (but note, in this case, that DMIM uses “PERT”, and that would sway me to SUBJ over COMP since I can’t use PERT in CDA R2).