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COVID, test reason and specimen

Hi all,

What are the best ways to store specimen and reason for testing associated with COVID test and to link it back to the original COVID test?

Test: COVID-19 Qualitative RNA test
Result: Detected
Testing reason: surveillance, symptomatic (one of the 2 values)
Specimen: Nasopharynx

1st record. Measurement.
Measurement_concept_id = COVID-19 Qualitative RNA test
Value_as_concept_id = Detected
2nd record: Observation
Observation_concept_id: 40769732 (Reason for test or procedure) Observation LOINC
Value_as_conсept_id: 1177348 (Surveillance report) Meas Value LOINC
3rd record option A: Specimen
Specimen_concept_id = Nasopharynx
OR 3rd record option B. Measurement:
Measurement_concept_id: 3015746 (Specimen source identified) Measurement Loinc
Value_as_concept_id: Nasopharynx

If to create 1, 2, 3 option B, then we could use observation.observation_of_event_id and measurement.modifier_of_event_id fields to link the associated specimen and test reasons to main COVID record. But I don’t know if it is a good idea to use Measurement instead of Specimen table.

Or we could create 1, 2, 3 option A and to use Fact_relationship table.

Where would you store test reason and speicmen and how would you link it to the main COVID test?

The OMOP oncology extension proposal includes MEASUREMENT table change by adding modifiers.
Thus, a measurement (cancer grade, for example) is a modifier of a Condition (cancer diagnosis).

In the case above Specimen and Observation are modifiers of Measurement.
So, should Specimen and Observation tables have modifiers to be added?

Or we just use fact_relationship for this purpose?

Is there a good reason to keep it separately (sampling date, anatomic site, amount)? Otherwise, it might be a part of the Measurement concept’s semantics.