Urine drug screens are often confusing if you don’t interpret them on a regular basis. I think a big reason for confusion is a lack of education on what these tools can do and what they look at. I would definitely classify myself as needing to learn more about drug screen interpretation.
The case: A 54 year old male presents with the following medication list.
- Gabapentin 300 mg TID
- Aspirin 81 mg daily
- Ibuprofen 400 mg BID prn
- MS Contin 30 mg BID
He states good adherence to his medications and gets them filled on a regular basis. He does however rarely use the prn Ibuprofen. Because of the use of his opioid, he has entered into a “pain contract” with his primary provider. This involves urine drug screening. Upon his urine drug screen, his results reveal that it is negative for all opioids. So what gives?
There are three major things I’m going to think about first in this situation.
- Test error. Lab errors are rare, but we need to recognize this as part of the differential in explaining what is going on. We have to at least consider that the lab results maybe in error for some reason. This should be investigated and a possible retest done.
- Drug Diversion. I really like to give people the benefit of the doubt, but it would be very important to look at this patient’s past history. We have to consider that the medications being prescribed for this patients pain might be up for sale or possibly being given to a family member or friend with an addiction problem.
- The experience in working with this patient would be incredibly important. Have they been trustworthy in the past, are there other things going on in this patient’s life that might present warning signs that a patient is not using their medication appropriately?
Want more clinical pharmacy pearls? Do you want them for free? Click here to check out 30 medication mistakes I commonly see in my practice as a clinical pharmacist!
I think a post on which drugs will show up on which opioid drug tests would be awesome – i.e. which are in the morphine pathway, hydrocodone, etc.
I will have to put that on the list! – Thanks for the idea! – Eric
There may be an error on the instrument; it could be that it pipetted a bubble, it may be mislabeled and the wrong urine test performed. It could be a pre analytical error or an analytic error. They normally will run one urine drug test and freeze the other one.
I find it odd that this patient does not have a prn morphine dose. To me, that suggests that maybe his morphine dose is too high and could be titrated down.