Observation - PDC scores

PDC scores for multiple medications for the treatment of a disease => this could be a two different types of diseases.

What is the FHIR guidance on how these should be handled?

Although your question lacks context and clarity, I assume you are asking why Observation value is not a list?

Use Observation component for multipart values to an observation or multiple Observations. It depend upon whether each Observation can be an independent stand alone observation or whether the results are only of value when reported together.

I understand. What I was trying to ask is as follows -

I have PDC score value as 0.8 for Disease 1 , PDC score value of 0.9 for Disease 2.

How do I represent these two scores in Observation resource?
Option 1) Can I capture the Disease name as part of the Observation resource itself e.g. category?

Option 2) Do I need to build a Condition resource to capture two diseases as follows:
a) Disease 1 as Condition resource and link it to an Observation resource as an evidence.
b) Disease 2 as Condition resource and link it to an Observation resource as an evidence.

I hope I have provided some clarity.

For complex observations that require multiple values to describe, we use Observation.component. So, for example, for a microbiology test the Observation.value might say “susceptable” and an Observation.component.value would identify the product the organism is suceptable to. This seems like the same sort of situation. The 0.8 would go in Observation.value and there’d be an Observation.component where the code + value identified the disease the PDC was measuring.

That seems doable, thank you very much for the guidance!

Hey, I wanted to reopen this discussion with some more details. PDC (Proportion of days covered), in its simplest form, is a numeric score calculated for a given medication a patient is supposed to be taking. If I am taking two different medications, I will have two separate PDC scores, one for medication A and one for medication B. It can also be associated with a condition, rather than a given medication.

I see a few different ways for representing this in Observation.

  1. Observation.code = “PDC” (forgive my shortcut notation), Observation.valueQuantity.value = 0.8, Observation.focus = { “reference”: “id”, “type”: “medication” } (or condition)
  2. Observation.code = “PDC”, Observation.valueQuantity.value = 0.8, Observation.component.valueString.value = “medication name” (or condition)
  3. Make an extension to Observation to include the ability to include a medication name or condition name as a proprietary extension, since this is something that is rather pharmacy specific.

My preference would be to use the focus property for this, so my question to the community is whether or not this is deviating from the intended purpose of that property. Given that the description for focus includes: “…The focus of an observation could also be an existing condition…” this seems like it could be a good fit.

My recommendation would be:
Observation.component.code=“medication” (or “condition”)
Observation.component.valueCodeableConcept = code for medication or condition

If you wanted to link it to a particular MedicationRequest or Condition as well with a focus you could, but there wouldn’t necessarily always be a Condition resource (or only one Condition resource) or necessarily a MedicationRequest to point at. If the PDC was intended to specifically be a statement about a single resource, then I guess you could eliminate the need for the Observation.component.