Understanding False Positives on Drug Tests

Drug Tests
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Have you ever been asked to take a drug test? Maybe it caught you by surprise, but employee drug tests have been a common practice in many industries for decades.

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They’re also required after vehicle accidents, criminal activity, during probation, as well as from healthcare workers, athletes, and students.

With the ongoing opioid crisis, drug screenings have become a priority for employers and HR professionals. Many companies are revisiting their policies because of reports showing that employees are failing these screening at higher rates.

With the increased interest comes a greater awareness of the limitation of testing procedures, including false positive test results.

Data suggests that as much as 5 to 10 percent of drug tests can result in false positives and may increase with the expansion of drugs included in the screening programs.

Why Do Employers Require Workplace Drug Screening?

The answer to this question varies by employer. Some industries, especially those that have to do with public safety, have to follow regulations that demand they perform drug testing on their employees.

Drug tests, whether they’re mandated or discretionary, have the following purposes:

  • Safety – An employee who’s under the influence of alcohol or drugs has a higher risk of accidents that could endanger them as well as their coworkers.
  • Security – Drug screenings can help detect and prevent employees who might engage in embezzlement or other forms of theft to finance drug addictions.
  • Liability – If a company’s employees are intoxicated when they came into contact with clients or customers, this might expose the company to legal action.
  • Reputation – Employees represent their companies, so any drug-related issues might hurt the company’s reputation.

How Are Drug Tests Performed?

The first stage of the drug screening process involves initial immunoassays, which are quick and can be performed on a large scale at a minimal cost. A specimen is collected – typically urine, but saliva and hair can also be used for drug tests.  

Most often, the specimen is collected at the test location. Although direct observation of the urine collection is not allowed, technicians may accompany the person being tested to the restroom, listen and check the appearance of the specimen as precautionary measures against tampering or substitution.

Once the technician receives the specimen, it will be divided in half. One half will be used to perform the test, and the other will be set aside to confirm a positive result or if there are any issues related to the test results such as error or contamination.  

False Positives

As we mentioned, the initial immunoassays are quick and inexpensive. They involve paper strips with antibodies, similar to pregnancy tests. The paper will react by changing color when it comes into contact with certain drugs and their metabolites.

Much like pregnancy tests, these tests can also give false positives when they detect a substance that is chemically similar to the targeted drugs. These substances could be from medications, supplements, and there are even certain foods that cause false positive drug test.

Producers of immunoassays are aware of these limitations and are always refining their test panels to reduce the number of false positives. However, false positives will always be an issue during the first stage of the screening process. Since the consequences of a positive drug test are serious, a second confirmatory test is performed on the portion of the specimen that was set aside – the GC-MS or Gas Chromatography Mass Spectrometry test.

The GC-MS test is much more specific and can rule out false positives, which is why it’s considered “gold-standard” in drug screening.

Drug Tests
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