Will urine drug testing show a false positive from my prescription medications?
It is possible in some circumstances to get a false positive result from urine drug testing because of prescription or over the counter drug use. In particular,immunoassay tests used for initial screening may indicate false positive results. However, there are mechanisms in place to prevent an employee from being penalized due to a valid prescription drug.
Urine drug tests are designed to detect the chemical signatures of the targeted drugs and metabolites of those drugs. A drug metabolite is the smaller chemical components of a drug that result from the body’s metabolism or breaking down of the drug following exposure.
A false positive result may occur when a prescription drug or other substance that is chemically similar to the targeted drug or drug metabolite is present in the urine sample. For instance, ephedrine and methamphetamine are chemically similar. Therefore, the use of ephedrine based over the counter medications may trigger a false positive result for methamphetamine use. A substance that triggers a positive result due to its similarity to the targeted drug is said to be cross reactive with that drug.
In most circumstances, an initial positive result from an immunoassay test will be confirmed using a more sensitive gas chromatography/mass spectrometry (GC/MS) test. Often this test will reveal the differences between the chemical substances and negate the initial test’s positive outcome. In other instances, further investigation may be necessary.
For employees covered by Department of Transportation (DOT) guidelines, a positive confirmation test must be evaluated by a medical review officer (MRO). The tested employee will be given an opportunity to discuss a positive result with the MRO and provide information regarding prescriptions or other authorized drug use that would explain the results. The MRO has the authority classify a urine drug test result as negative if he or she determines that there is a medically valid explanation for the non-negative test result.
An employee should make a list any prescription or over the counter drugs that her or she is taking at the time of testing so that this list can be provided to the MRO if necessary. Because of the need for anonymity, this information cannot be provided on the Federal Drug Testing Custody and Control Form (CCF). Therefore, the employee should make his or her notes on a separate piece of paper.
Written by Shauna Krahn
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