positive cocaine screen, but negative on confirmatory test

[annie501]

---

Members do not see this ad.

I have a patient who recently tested positive for cocaine on a drug screen. She swore up and down to me that she does not use cocaine, doesn't know anyone who uses cocaine, etc. Well, I sent a confirmatory test, and it came back negative. I am not quite sure what to do with these results now. Do I assume that in fact, she is not using cocaine? Does anyone know of anything that could cause a false-positive on the screen (or a false negative on the confirmatory test)?
I know that the screen tests for benzoylecgonine. I don't know much about the confirmatory test.

 

[deleted77919]

…

 

[goldennugget]

There aren't that many things that cause false positives for cocaine, unless the patient was using some sort of topical anesthetic that might have low amounts of cocaine in it. Because the GCMS confirmatory test is very accurate, I would say that she did not use cocaine (provided that the urine samples for the typical UDS and the GCMS were provided at the same time.

 

[annie501]

Thank you for the help. I still wish I knew exactly what happened here, but I really appreciate the input.

 

[OldPsychDoc]

Sometimes a false pos is just a false pos...

 

[annie501]

True.

 

[doctor4ever]

Here's a very good review article on the subject.

http://download.journals.elsevierhealth.com/pdfs/journals/0025-6196/PIIS0025619611611208.pdf