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EHR Prescription data - best practice

Hi all, We(UTSW) had some questions around prescription data from the EHR. what is the correct value for days_supply when prescription has refills. Also, if we have junk data in the days_supply - what would the cut-off be?


Hello @Amira_utsw,

Per the conventions, the days supply field in Drug Exposure: “This should be the verbatim days_supply as given on the prescription”. You take the days supply # from the source as is (exceptions noted below). Don’t do any math with the refills. The refill data will be ETL’d to the refill column.

As an example, a person receiving Lisinopril for high blood pressure will usually get a prescription with days supply = 30 days or 90 days. The person receiving the 30 days supply will have refills = 12 or a full years worth of medication and the person receiving the 90 day supply will get 4 refills for a full year of medication. Put the 30 or the 90 in the days supply field. Then put the number of refills in the refill field. When the supply and refills run out, the person goes back to the doctor for the checkup, still has high blood pressure condition and the cycle starts again.

For the researcher, unless they are studying how providers order drugs, these columns most likely won’t be used. Most researchers (and the OHDSI tools) look to the drug start and end dates to find the duration of use for a particular drug of interest.

We all do! But definitely those of us with EHR data have a lot of cleaning before OMOPing!

Any negative number should definitely go in the garbage can. Should you just exclude the days supply for such a record? Or toss the whole record? That is up to you since you know your data the best. As for the upper limit, there isn’t an OHDSI convention and in Colorado, we didn’t create an upper limit. Looking at our source data, our top 10 values for days supply are as expected. But we do have days supply values > 3650 (10 years) and these must be typos and should be excluded. I’m tagging this topic with #themis. Themis should clarify the documentation and add in some guidelines for acceptable values for the days supply field.