Diagnostics request template structure

New to openEHR?
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Hi everyone,
I’m new-ish to openEHR and I’m cutting my teeth in the diagnostics domain as this is what I’ve worked in the past few years (HL7v2 primarily). I am attempting to build a test request template, based around the openEHR-EHR-INSTRUCTION.service_request-laboratory_test.v0 archetype (https://ckm.openehr.org/ckm/archetypes/1013.1.7230). I appreciate this may not be the best starting point, (service_request_v1 may be better) but I think the question still stands.
I’ve hit a conceptual barrier in that I’m not sure how to handle a request that may have multiple specific tests (eg 1:TB confirmation 2:TB species identification and 2:TB sensitivities) but only 1 specimen. One or more of these may be requested, depending on what has been already performed or is known at the requesting site.
I can see that I can have multiple ‘current activities’ (ie one for each specific test). This pattern has a child of ‘Requested specimen’, but the specimen is the same across all tests and I don’t think I want the specimen details to be required once for each test, so adding a openEHR-EHR-CLUSTER.specimen.v1 to the ‘protocol’ section would make sense to me, however I am unclear about how I can reference this from each requested test. I’ve done some searching in this forum and not found anything that appears related to this.
So, my questions are along the lines of:
Is this a reasonable approach & if so how would I refer to the common root/protocol/specimen from each specific root/activities/current activity/description/Service name/code?
Should I just accept the repetition and deal with it in the UI (yuck!)?
Have I missed the (or multiple!) point completely and I should do more reading somewhere?
Is this a question that hasn’t been resolved yet? There are other potential patterns (eg 1 test, multiple specimens seems OK, multiple tests with multiple specimens is also a rare edge case) that can happen

Apologies if this question has been poorly framed - I’m more than happy to be told to go and read an idiots guide and try again!

Many thanks

Andy

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Not sure why you deleted your post @Andy_Harris I thought it was a very good question - as I understood it , how to handle e.g multiple lab test requests from a single Service request.

You could certainly multiple activities but that does feel clunky. I thin there is a case for the Service Name element being made multiple to allow for this possibility.

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Thanks Ian
I’m not sure either - I’d like to blame it on an errant cat, but I don’t have one. I’ll just have to put it down to PEBKAC. I’ve undeleted.

HL7v2.~4 onwards takes a similar hierarchical approach in that different message types have either an order(ORC/OBR) with nested specimen(SPM) or SPM with nested ORC/OBR
In FHIR, it’s possible to do this using a reference element that points to the Guid of a specimen resource (or vice-versa) and I like this as it’s explicit and allows for multiplicity in either direction. I have done a bit more reading and have found Data Types Information Model (dv_ehr_uri) which I presume allows a pointer to an external (pre-existing?) composition. There doesn’t appear to be an equivalent for an internal reference (eg this/…/specimen/external identifier/), though this may be precluded as a template/archetype is empty of values (whereas a FHIR resource is referring to stuff that already exists). It may be enough to provide a URI slot and then use a GDL statement at runtime to force/validate that the test points at a valid specimen within the composition?

So my thoughts at the moment are - an internal URI/link is likely the best approach, though internal referencing is not currently supported (possibly for good reasons) and so this means different archetype/template hierarchies (similar to v2) depending on the actual diagnostics detail?