Are there loopholes in workplace drug testing?

I received a phone call the other day from a recruitment advisor from one of our large clients in mining. She was concerned because she had just received the results from one of our KINNECT Pre Employment Medical Assessments.

The results seemed to be conflicting because the instant urine drug screen cup said the applicant was ‘non-negative’ but the lab results said he was ‘negative’.

Normally, a simple explanation about the difference between the instant urine drug screen and laboratory drug testing would suffice. However, I was curious to know which drug classes we were discussing. The recruitment advisor told me that the drug class was cannabis (THC) and that she couldn’t understand how an instant urine drug Screen was “non-negative” (positive or present) for cannabis but that the lab result was negative (or absent) for cannabis.

Then I understood her concern. These seemingly conflicting results create questions like, “Which result should I believe – the instant result or the lab result?” and, “Is THC in the applicant’s system or not?”

The answer to this question lies in the levels at which individual drug classes are detected by the instant drug screen cup and the laboratory test. These levels of detection or “cut offs” are according to Australian Standards and, in the case of THC, this cut off is 50ng/mL. So theoretically, if the concentration of THC in the applicant’s urine is less than 50ng/mL, the drug is not detected and it is considered a negative result, but if concentration of THC is above 50ng/mL, it is detected and it is considered a non-negative (positive) result.

But we do not live in a perfect world and nothing is black and white.  So something as simple as Drug And Alcohol Testing is not that simple.  There is more.

The cups that are used for instant drug screens have an error of plus or minor 25%. That means THC concentrations below 37ng/mL are considered a negative result and concentrations above 63ng/mL are considered a non-negative result, but concentrations between 37ng/mL and 63ng/mL could go either way.

If you are looking for a definition for ‘conundrum’ this could well be it. However, at these levels THC concentrations are still very low.

Laboratory testing has a much higher degree of accuracy and would come a lot closer to detecting the absolute level of THC in the applicant’s urine to the nearest ng/mL which is why we send non-negative samples to a laboratory for GC/MS confirmatory testing. However, because the level of THC in the urine sample collected from the applicant in this case was determined by laboratory testing to be below the cut off of 50ng/mL, it was reported as “negative”.

So was the THC present in the applicant’s urine? Most likely.

Was there enough THC present in the applicant’s urine to be absolutely, 100% sure? No.

So what is the point of performing an instant drug screen and why should we pay for confirmatory testing by the lab?

Good question. Remember, any instant drug screen, whether the sample is saliva, blood or urine, is important for instantly detecting the presence or absence of a drug or its metabolites. This is an important step and is a much quicker and cheaper option than simply sending all biological samples to the laboratory for testing.

However, for samples where drugs or their metabolites are shown to be present by an instant drug screen, laboratory testing will confirm whether these levels are “therapeutic” in their concentration or “recreational”. Both pieces of information are still very important for employers and recruitment officers and help determine a worker’s fitness for work.

Unfortunately, this time the levels of THC in the applicant’s urine were too low to determine for sure whether he had THC in his system or not. If there is a loophole in instant drug screens and in laboratory drug testing, it is a very small one indeed. I guess the standards and processes surrounding drug and alcohol testing are ultimately designed to avoid making clinical errors and therefore, errors in judging a worker’ s fitness for work.