[AngieAndxretti]

I recently failed an oral swab drug test for cocaine without having ever used it.  The test was confirmed with gas chromatography, and those results were given to me on a printout from LabCorp.  The printout lists a positive result for cocaine itself at a level of 43ng/ml and a negative result for benzoylecgonine at zero ng/ml (it doesn't just say negative as-in below the cutoff of 20ng/ml, it actually says zero ng/ml.)

Question: How can one test positive for cocaine but have zero of the primary metabolite present?  Is that really as weird as it seems to me?  Does the lack of the metabolite mean that my sample was contaminated by someone who handled it, like in the case of someone having cocaine on their hands?  What are the possible explanations for this test result?

I've read elsewhere that tonic water can cause false positives for cocaine and I drink the stuff all day, but given the gas chromatography confirmation it is impossible for the tonic water to be the cause, correct?

Right now I'm looking at losing access to my medication because of this test result.  My doctor did order a hair test, stating that I "might" be able to stay if I pass that test but I don't expect the results for at least a week and this is keeping me up nights in the meantime.  I sure hope I pass the hair test, and that my constant ingestion of tonic water doesn't interfere with the results but I'm very concerned about the whole situation.

Does anyone have any thoughts, especially on the original strange test result?

[Mitch]

It's not tonic water, but likely related to the other medications you are taking. Do you mind sharing what medicines, herbal remedies, supplements, and vitamins you are taking?

[AngieAndxretti]

Well the situation is resolved now because I did pass that hair test that was offered to me.  It cost me $200 to prove my innocence and I didn't even get an apology for all the anxiety this caused me but I did get a firm handshake at the end of my next visit which is actually a lot from this particular medical practice.

I still don't know what caused the false positive although I've come to suspect that the nurse who handled my oral swab may have had cocaine residue on her hands and touched the tip of the swab before handing it to me.  I've seen them do it, as I've been watching for stuff like this since this experience.  They often touch the part of the swab that goes in my mouth with their bare hands when they rip open the package.  I've complained about it of course, but I've learned I have to watch everything like a hawk because I have so much to lose here.

I'm still curious about any alternative explanation so I'll list my meds as requested:  Methadone, Prozac, Synthroid, Estrodiol, Cyproterone Acetate.  All of these meds and their doses have remained constant throughout years of negative tests.  I take no herbal supplements.  I drink one red bull every morning and lots of tonic water throughout the day.

[Arkcon]

In the future, see if you can specify to the powers that be that swabs and specimen cups be given to you sealed, and the seal broken by you before use.  While it seems very far-fetched that the nurse would have contaminant on their hands, its still basic specimen control to have you be given sealed implements, and you break the seal before you use it.  Heck, they even do that for tests I get for health diagnostics, which makes the opportunity for contamination in your case simply baffling.

[Mitch]

@Arkon, I don't think it is far-fetched at all that a nurse would have cocaine residue on her hands. I think that is the most likely culprit in this scenario. Cocaine is often found on money after all.

[Babcock_Hall]

There are a couple of studies of cross-contamination via gloves in PCR-based DNA profiling.  The amounts might be on the picomole level.