Drug Testing Laboratory Accuracy

Today’s guest post is from Dr. Charlton Owensby, Medical Review Officer (MRO) for WOLFE. Dr. Owensby is an AAMRO-accredited Medical Review Officer. He has been an MRO for more than 25 years. He is both a physician and a lawyer.  This dual perspective provides a unique understanding of the consequences of what happens to all parties when the drug testing process is done incorrectly.


The certified laboratories that perform work related drug testing are very good at what they do. I’ve reviewed the laboratory results of many tens of thousands of drug screen tests over almost twenty five years and I’m impressed that the process of testing for substances of abuse from collection to testing and reporting works so well.  Lest you think I’m a lab toady, I don’t work for any testing laboratory though I do work closely with most of them.

If you noticed, I did limit my platitudes to ‘certified’ laboratories – those laboratories certified by SAMHSA or the College of American Pathologists (CAP). There are a number of other entities who claim all sorts of competence measuring, testing and reporting on all sorts of things without these certifications but I won’t do business with them as I don’t consider them reliable – and my reputation depends upon a competent testing laboratory.

A professional certified laboratory can be a wonder of automation, logistics, expertise and proud scientists. In order to achieve certification they have to continuously demonstrate laboratory competence and subject themselves to review and inspections from outside institutions. They agree to blind sample testing to make sure their operations are consistent, accurate and valid. (Blind sample testing involves a third party, unknown to the laboratory, sending in known specimens prepared to be positive for a substance. The laboratory has no idea which samples are blind samples among the hundreds or thousands of tests performed. The laboratory results are compared to the known sample to determine if the laboratory is testing and reporting accurately.)

Something that is not really talked about is the bias toward a non-positive result in these professional laboratories. By that I mean everything has to line up just so in order to call a sample result positive – the seals on the sample must be intact, the internal sample validity testing must be acceptable, and the screening and confirmatory testing must agree at the appropriate levels. This bias serves to protect both the employer client and the donor employee and it all but ensures that a positive result is a positive result.

OK – do certified laboratories make mistakes? Yes. I have direct knowledge of two instances of a false positive report (from two different laboratories and for different substances), and I’ve heard from reliable sources of two other false positives. Keep in mind that’s over twenty five years and tens of thousands of tests. Undoubtedly there are others, but I expect at about the same ratio of false positives to total tests across all certified laboratories.

Think about that for a minute – not the low incidence of false positives, but that there are any at all. To have a false positive means there was further testing that showed the initial test was in error – that means someone (most likely the donor) knew that something was wrong and requested that sample be tested at another certified laboratory, and there it failed to confirm the first test. The second certified laboratory tests the ‘positive’ sample not to a threshold standard but  to the equipment ‘limits of detection’ meaning if any detectable substance is present the test is confirmed, if no substance is detected then the sample will fail to re-confirm the initial test. That is a very robust system to protect the company client and donor, although it can cause some anxious times for both. I am of the opinion that all employment drug tests should have this confirmatory back up available – another reason to use a certified laboratory.

The original testing laboratory does not get off easy. Upon learning of the failure to confirm one of their positive reported samples lots of things happen quickly. The laboratory will retest the original sample, review all the logs for the equipment loading and equipment performance, may retest whole carousels of samples to confirm all the results of each sample, and prepare a report on what happened and how to prevent it again to their certifying authority. My impression is the equipment rarely fails without a lot of notice to the operators; rather the operator generally put a sample in the wrong place, pipetted the wrong sample, or mislabeled a specimen. It’s actually hard to make these mistakes given the bar codes and logs that have to be signed off multiple times for each testing run. But once every thirty or forty thousand times it may happen…

Addendum: What about false negative results? I would expect there are some of those as well – but we’ll probably never know since no donor is going to challenge a negative test. At that point the drug test becomes an IQ test and the donor has given you two good reasons not to hire him.



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