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Urine Color or Clarity Lab result values in Observation or Measurement depending on how they are mapped

Can someone enlighten me why the same term depending on which codesystem is mapped to it would be transformed into Measurement Table or Observation Table?

Example: Urine Color (part of a Urinalysis panel lab order) reported as a lab result (LOINC encoded) and it’s value (Amber, Yellow, Red) which would be mapped in the US (per USCDI) to SNOMED CT Qualifier Value codes and ETL into OMOP Observation Table.

The same Urine color value of Amber, Red, Yellow, etc. if mapped to a LOINC Answer Code would ETL into OMOP Measurement Table.
(Also laboratory medicine does not make the distinctions of lab result into Measurement and Observation, but I realize others outside of laboratory medicine like to categorize results and their values as seen here into different tables. Hence the issue.)

Was there a reason OMOP decided to split the same item into 2 different tables? It seems if users are not aware, they can miss a portion of lab results with their queries/analyses. With multicenter studies, they’d have to query both not knowing how an individual site may have mapped this term to ensure it’s included in all cases.

Also given USCDI lists SNOMED CT Qualififer values as the codesystem standard for qualitative result values, it would be nice if they were in the same table as the results from which they originate. It would be nice if all lab results were in the same table too.

Thank you for helping me to understand the why behind this design.

Hello, @apitkus. In OMOP we use measurement-result pairs. We try to measure something and get some result (answer). And the answer can only reflect to measurement, but not to another answer.
In the first case Urinalysis is Measurement and Urine color is Answer (result). In this case it’s value (Amber, Yellow, etc. can not belong to Answer (result), because it would appear that one answer belongs to another, and it does not make sense. So it should be Observation.
On the other hand, in the second case Urine color is the measurement, and value of Amber, Red etc is the answer.