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Advice on how to map oral glucose tolerance test measurements at specific time points that do not have standard ids

Hello OHDSI community, I am very happy to join in! I am currently working on Mapping measurements from oral glucose tolerance tests (oGTT). There we take a blood sample at baseline, then administer a liquid containing glucose and take blood samples after 30, 60, 90 and 120 minutes in order to measure blood glucose at the different time intervals.

What has been done: I was able to find standard ids for fasting blood glucose measurements (4156660 - "Fasting blood glucose measurement), the 1 hour time interval (40482677 - “Measurement of glucose 1 hour after glucose challenge for glucose tolerance test”) and the 2 hour time interval (4176733 - “Measurement of glucose 2 hours after glucose challenge for glucose tolerance test”).

Problem: What I cannot seem to find are standard ids for the glucose measurements at the 30 and 90 minute time interval.

Question: How do I best map the glucose measurements at the time intervals after 30 and 90 minutes? Do I simply do that by setting the measurement_concept_id to 0 or can I do it in a more sophisticated way?

Proposed Ideas: I can think of setting the OGTT as an observation instead of a measurement and use qualifiers (there is one for 30 but not for 90 minutes: 4114365 - " 30 minutes post-dose"). Another alternative could be to work through the measurment_datetime or measurement_time field in the Measurement table. However, I only have the date and not the time of the measurement, I would need to set an arbitrary time point and increase the time interval from there.

Does anybody have experience with this kind of Mapping and/or has any tips or advice to provide? I am very grateful for any ideas!

Thanks
Ivona

Hello, @ivona. Welcome to OHDSI

In the Measurement domain, LOINC vocabulary is usually much more specific than SNOMED, so I advise you to switch to LOINC. Your concepts may be mapped in the following way:

Glucose [Mass/volume] in Serum or Plasma --pre XXX challenge
Glucose [Mass/volume] in Serum or Plasma --30 minutes post XXX challenge
Glucose [Mass/volume] in Serum or Plasma --1 hour post XXX challenge
Glucose [Mass/volume] in Serum or Plasma --1.5 hours post XXX challenge
Glucose [Mass/volume] in Serum or Plasma --2 hours post XXX challenge

And even better: browsing LOINC, you would be able to find more specific OGTT (like 75 g glucose PO), the concepts above are just a good generic examples. Check this hierarchical concept:

Glucose | Serum or Plasma | Chemistry - challenge

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