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Defining interval period between 2 same blood test within a week before index date of a drug exposure


#1

Hi,

I want to define a cohort which says warfarin use and outcomes. for which I need to look for consequent 2 INR measure blood tests which is done within 1 week before index date of starting warfarin and with at least 1 day interval between two inr tests.

Qestion : For above case how can i define interval of at least one day between two inr tests within a week before starting warfarin using atlas ?

Kindly guide. Thanks in advance!!


(Chris Knoll) #2

You’d use nested criteria for this:

Having at least 1:
  INR Test
    having at least 1: <-- this is the nested criteria
      INR Test
   betwwen 1 days after and all days after <- this index refers to the INR test
between 7d before index and 0d before index <- this index refers to the warfarin exposure

You could be looking to do something later such as ‘and some change between the two measurements’ You can’t do this using the Atlas cohort definition tool.

If the change in measurement value would lead to a condition diagnosis, then use that fact instead of looking for a change in measurement value.

Update:

I may not have understood your question properly: are you saying you want to find warfarin users that have had 2 distinct INR measurements, or are you just trying to define an outcome cohort of ‘2 distinct INR measurements’? The way I interpreted your question was that you were looking for warfarin exposed with INR measurements.

If you are looking for an outcome of INR measurements, then you can just define a cohort of the INR measurements, but you need to be clear about which date (the first INR or the second INR) is the ‘cohort start date’ of your outcome.


#3

Thanks Chris!

You have rightly understood my question. I am looking for patients who were exposed to warfarin after having 2 inr tests with abnormal result and with at least 1 day interval between 2 tests within a week before starting warfarin.

Could you please send Json expression for setting Inr interwal? As I din’t get result using the above nested criteria.(graphical view differs after setting the above nested criteria).

Thanks in advance


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