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Family Physician
Family Physician, Board Certified MRO
Category: Drug Testing
Satisfied Customers: 2039
Experience:  Medical Review Officer - Physician Trained and certified in drug test interpretation
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I have a client who did a hair follicle test and it was

Customer Question

I have a client who did a hair follicle test and it was positive for cocaine. She says she has never tried cocaine. She recently went to her doctor and was diagnosed with a bladder or kidney infection. Could that cause a false positive?
JA: Is this a time sensitive issue? What type of specimen are they testing?
Customer: It is a time sensitive issue. The court took away her three year old son and gave him to a father that rarely sees him. Our court hearing is on December 8th. I don't know what type of specimen they are testing. I only know that it was a hair follicle test.
JA: Anything else in your medical history you think the doctor should know?
Customer: She is on antibiotics, but I'm not sure she was on them at the time of the testing. She says she went out and had some drinks with tonic water some time before the testing. That's really all I know. Are there medical conditions that could cause a false positive for cocaine on a hair follicle test?
Submitted: 9 months ago.
Category: Drug Testing
Expert:  Dr. D. Love replied 9 months ago.

Hello from JustAnswer.

Do you have a copy of the test report?

If so, can you attach a copy of the report (after blocking out her name and any other identifying information)?

Expert:  Dr. D. Love replied 9 months ago.

I had asked for some additional information and have not heard back, so I will explain why this additional information is important.

The issue in this situation is what type of hair follicle drug test was done.

A false positive is really on pertinent when discussing drug screening tests. There are two general categories of drug tests, whether done on hair, urine or any other specimen. The first category are drug screening tests, which are primarily immunoassay tests. The second category are confirmatory or definitive tests, and these are primarily chromatographic/spectrometry tests, such as gas chromatography and mass spectrometry (GC/MS)

A common process is to first perform the screening tests and then only do the confirmatory test if the screening tests is positive. The screening tests are cheap and fast, while the confirmatory tests are lengthy and expensive, and getting a negative screening test will avoid the cost and time to do the confirmatory test.

The screening drug tests have a fair amount of false positives, sometimes because of another drug or substance that we know can cause false positives, but also sometimes in people that are not taking any other substances. However, these same drugs or substances will not cause a false positive on the confirmatory test. In fact, it is the confirmatory test that is negative after an initial positive screening drug test that proves that positive screening drug test was false.

Within that context, there has been some discussion in the literature that certain antibiotics may cause a false positive on screening drug tests, but there is no clinical study that has confirmed it. But in reality, false positives can occur anyway, and it does not matter what is causing the false positive. When there is a false positive, then the confirmatory test would be negative, and that is sufficient proof that the initial positive screening drug test was false.

If the lab did a confirmatory drug test, then there is no medicine or illness that would cause a false positive.

The terminology for the various drug tests varies from one lab to another, which is why I asked if you had a copy of the report.

I also asked for the report because of another issue that is worth noting. Since the hair is exposed to the environment, someone can get a postiive result from environmental contamination. However, this can be identified by what was detected on the drug test. If the test detected cocaine alone, then it would be environmental contamination. However, if the primary metabolite of cocaine, called benzoylecgonine, is also detected on the hair drug test, then that indicates that the cocaine must have been metabolized in the body, so could not possibly be due to environmental contamination.

So, do you have a copy of the test result?

If not, can you get a copy of the test result?