False Positive Testing for Illegal Drug Use

Someone asked about cross reactivity with prescribed and over the counter medications in a positive test for cocaine in a patient denying any exposure to it. 

The list is very long. 

The first thing I ask people to do is to test a glass of water from the  tap. If it is positive for cocaine, the testing is a bit faulty. But, who knows with Schuylkill County? There could be so much metabolite of cocaine put out by people just peeing, the tap could be positive for cocaine. It is not removed by sewage treatment. We are  all on everyone' s meds and their urinary metabolites. I would not even trust Deer Park bottled water. This review is a bummer. 

https://www.focusforhealth.org/drinking-prescription-drugs-tap-water/

Then, I would request the lab provide that list. It includes local anesthetics for toothaches. They are chemically related. 

This list is only the beginning, from our friends at GoodRx.com

https://www.goodrx.com/blog/these-15-medications-can-cause-a-false-positive-on-drug-tests/


If this does not provide relief, I would request the following, which I cannot even pronounce:

Here are the names of the test that should be done on blood or urine to confirm the presence of cocaine.

 gas chromatography (GC), gas chromatography - mass spectrometry (GC-MS) or liquid chromatography/mass spectrometry/ mass spectrometry (LC-MS/MS). The subsequent confirmatory procedures are performed on a second independent portion of the original urine specimen.

It may cost $100's if not a $1000.

CPT Code(s)**

80353 (HCPCS: G0480)

Methodology

Gas Chromatography/Mass Spectrometry (GC/MS)​