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How Do False Positives Occur on Drug Tests?

photo of a medical technologist conducting drug testingIf you or a loved one has had a positive drug test, the most likely occurrence is that it’s actually positive. False positives are extremely rare on many drug tests. But, in some very rare occasions, tests can show up as false positives. Here, someone is flagged as having a substance in their blood indicating drug use – normally from a substance that breaks down in similar ways or which creates the same substances. In addition, other flukes, such as mislabeling samples can result in false positives on a drug test.

While there are many ways false positives can occur on drug tests, there is a single way out of all of them. You can ask for a hair or nail test – which will conclusively show drug use – sometimes as long as a year ago. Because most employers will give you a retest, will request a more in-depth test, or will be willing to discuss with you – that’s the logical next step. In addition, some states actually offer laws allowing employees to request a re-assessment of a positive drug test.

However, if the drug test is for a loved one, it is critical that you approach them first. Chances are, a positive is a positive, and they are actually using. There are exceptions, but false positives are very rare.

How Do Workplace Drug Tests Work?

Most workplace drug tests use urine or saliva tests to assess whether someone has been using. These tests are, on average, accurate for 3-5 days after the last drug use –depending on the drug in question. Saliva and urine tests are the fastest, cheapest tests which can be run and are extremely accurate. In fact, every positive test has been run twice– with the same result.

How does that work?

In most cases, a lab analyst goes into the workplace and collects samples. Here, a cheek swab is the most likely. Samples are taken, inserted into a plastic tube, and labelled. Then, they’re sent to a lab for testing. Each tube is entered into the machine and then entered into an immunoassay test. The biological sample is split into two, for an initial test and a confirmation test. If the first immunoassay test comes up positive, the lab runs a second type of test to verify results.  The second test, a Gas Chromatography Mass Spectrometry (GC-MS), is a more thorough test, and is more likely to have a false negative than the initial test. In addition, if your result is not screened using a GC-MS test, your employer is legally required to grant it to you. If both tests are positive, the lab reports a positive drug test.

Get Your Questions Answered

What Scenarios Result in False Positives?

So, what can go wrong here? In most cases, there are just two scenarios in which something could go wrong.

Human Error – If the lab improperly labelled samples, you might be receiving someone else’s result. This is especially likely if there is more than one person in your workplace with the same or a similar name. It’s also slightly possible the lab inserted the wrong results into your screening. However, this is unlikely. The chance that it can happen means that some states protect your right to request a retest.

Contaminates – In some cases, you get a false positive because you’ve taken medication or consumed food that creates molecules and enzymes similar to those created by drugs. For example, nearly everyone is familiar with the poppy seed creating a false-positive for opiate use. Unfortunately, there are many things that can trigger a false positive. For example:

photo of colorful oral medications on white background

  • Ibuprofen
  • Fluoroquinolones
  • Vick’s Inhaler
  • Antibiotics
  • Anabolic Steroids
  • Benzphetamine
  • Brompheniramine
  • Coca Leaf Tea
  • Robitussin
  • Doxylamine
  • Diphenhydramine
  • Diet Pills
  • Labetalol
  • Hemp oil, some hemp foods
  • Nasal inhalers
  • Poppy seeds
  • Promethazine
  • Psuedophedrine
  • Setraline
  • Venlafaxine

This list is non-comprehensive. However, it should give you a good idea of what types of over the counter and prescription medication might trigger false positives. For this reason, many employers and labs encourage people getting a drug test to bring along a list of any medication they might be taking. This will be taken into account during the test to further reduce the chances of a false positives.

However, most labs are already very aware of which medications result in false positives. There are standard procedures in place to identify and screen out any known false positives. Therefore, it’s highly unlikely that you can consume a few bagels with poppy seeds and trigger a false positive. For example, labs now look at the cycle count and volume of the enzyme in the blood – which can’t be triggered by poppy seeds in the same volume until you eat several pounds of them. So, false positives because of contaminates are also relatively rare.

How Common Are False Positives?

False positives comprise some 1.75% of all blood tests, but up to 90% of false positives are simply showing the wrong drug. For example, MDMA usage frequently creates a false positive for amphetamine usage. The person triggers a false positive for amphetamine usage but was using MDMA. The further 10-50% of blood tests not attributed to drug confusions are almost entirely linked to human error. This means that you can easily request a retest. However, most employers will choose to retest using a hair or nail sample rather than saliva or urine. This is because hair and nails show a longer history of drug use, and you can’t fake it by simply not taking drugs for a few days.

Modern drug tests almost never result in false positives. GC-MS testing, including dual testing, often means that the chance of a false positive is close to 0%. If you do come up with a positive test result, it’s important to discuss it, ask your employer for a retest, and, if they are not cooperative, to pursue the issue with an employment lawyer. If you don’t use and you have a false positive, a hair or nail drug test will clear your name.

However, if the test is for a loved one, make sure you have an open discussion with them before taking steps. A hair or drug test showing a longer history of drug use could further incriminate them and make it more difficult for them to keep their job. If your loved one is using, their best next step would be to ask for help getting into rehab or treatment or to do so on their own. Many employers offer assistance programs, insurance providers are required to offer assistance on rehab, and you can take up to 90 days of unpaid leave from work to attend that rehab. However, if you do have a positive drug test, it may be too late to keep your job. That depends on your employer, the situations in which drugs were being used, and their policy.

Good luck with your false positive drug test.

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