While investigating an Atlas study which returned very few Persons, I found the Units for the specified Measurements in the inclusion criteria did not align with the Units for those Measurements in our source data. Upon further inspection of the source data, I found a Measurement could have 11 different unit_concept_ids. The Units for the Measurements of interest in Altas aligned with LOINC’s example Units for Measurements, as Dmytry links in this thread, however, real world data doesn’t always align with the suggestions.
How do we implement the “preferred” unit? Per Dima, “we need to create relationships from Measurement to preferred unit in concept_relationship table”.
The original numeric result & unit_source_concept_id aren’t represented (numeric_source_value and unit_source_value) in the Measurement table. See Vojtech’s github issue found here.
Recommendations:
Standardize the Unit for the top 375 Measurements identified in Vjotech’s study. Then as use cases arise, the community can submit issues to Github to include additional Measurements for Unit standardization.
Create relationships to preferred concepts in the Concept Relationship table.
Create a solution to store the original numeric results and units in the Measurement table.
Provide ETL guidance, on how to implement the value_as_number transformation for a unit_source_concept_id to the standardized unit_concept_id.
a. Community sourced conversion math? Researchers currently have to convert numeric results into a standard to run studies. We should glean this information from available resources.
@MPhilofsky Thanks for bringing it up again! Indeed, measurements are a huge pain in any study. I’d imagine that a large ETL effort would be needed to adopt standardization practices. Additional issue currently handled at the study design stage is dealing with measurements with no units and identifying implausibly high/low value-unit combinations.
Another intermediate option that would be beneficial to community is create a library of measurement-unit pairs that can serve as a reference (for example, as a part of PHOEBE recommender system). Seems that @Vojtech_Huser
has done most of the work for that, so now it’s a matter of pushing his knowledge base to a more convenient place.
I’m curious about this process. Some Measurements don’t necessarily need Units because there is usually only one associated Unit (heart rate), but others need Units to be interpreted correctly (weight) and others are more ambiguous. Is there a standardized approach for this?
you need a triplet. lab test, bad unit, preferred unit (and what you propose only takes a pair)
this is almost solved. But there is one field missing (it has been submitted to CDM repo) (orig. units I think)
there is AoU knowledge base for that. (I posted that link on the forum). N3C has also their solution to that (maybe also posted publicly somewhere)
Clair knows that this is something I am super motivated to submit PRs to DQD for. It was not on recent priority shortlist. I think that this item is the best way to nudge the network little by little. Super motivated for this fourth item.
It’s @Vojtech_Huser’s proposal, essentially. For each test, create a standard unit. During ETL all MEASUREMENT records would be normalized this standard, and for that two things need to happen:
Determination what unit is used in the source, if it is not clear. Which it often is not, believe it or not. In many cases, you can only guess from the distribution of value which unit it is likely to be.
Determination of the conversion factor.
But before we figure this out let’s plan on finishing the job of attaching standard units per LOINC concept.
This is a very important issue. I agree that harmonizing units and reference intervals is a worthwhile area of research. Another harmonization challenge is that an assay for a biological or chemical entity can have more than one concept. Consequently, different sites may use different concepts for the same measurement. I recommend creating measurement concept sets to improve semantic interoperability of data from the measurement domain, and have done some preliminary research with that idea. Please let me know if you would like to collaborate on measurement concept harmonization in OHDSI. @cukarthik
Nothing has been adopted by the OHDSI community due to the complexity of the issue.
In order to change the unit of a lab test via concept_relationship table, the value must also change accordingly. However, there are cases when the unit is not easily convertible.
The University of Colorado has implemented standard international units for vital signs (height, weight,etc.). We haven’t implemented standardized unit for lab tests because we have 1000’s of lab tests and many have > 1 unit associated with the test.
Here’s an oldie, but goodie paper on EHR lab tests and their associated units. It summarizes the complexity I speak about.
Melanie is correct. Nothing super formal (and formally ratified).
I, however, have a new motivation to put more effort into it (in 2024 context).
(during 2021-2023 it received a bit less of my attention as would be ideal).