How to Interpret a Urine Drug Test

Addiction medicine physicians discuss the different types of urine drug tests, false positives, invalid tests, and how to communicate results to patients.
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Carolyn A. Chan, MD: Welcome back to The Curbsiders addiction medicine podcast, where we use expert interviews to bring you clinical pearls and practice-changing knowledge on substance use disorders. I'm Dr Carolyn Chan, and I'm joined by my good friend, Dr Natalie Stahl. Can you tell the audience what we're going to be doing today?
Natalie Stahl, MD, MPH: We're going to recap recent episode number 18 on urine drug testing with our guest, Dr Timothy Wiegand from the University of Rochester.
Chan: He gave us so many great pearls, so be sure to check out the full podcast episode, Urine Drug Testing. Dr Wiegand reminded us that before we even order a urine drug test (UDT), we should be sure to let the patient know what the purpose of the test is and how it will be used to guide clinical care. Don't order a UDT if you don't have a purpose for it. When you have the results back, be sure to be supportive, not accusatory, and ask questions, particularly if there are unanticipated results.
Persons with substance use disorders have already experienced stigma in the healthcare system, so be sure to avoid stigmatizing language such as dirty and clean, and instead try to use terms like positive and negative when referring to UDT results. UDT results should be used to help support a patient in recovery, and the patient should be involved in the dialogue surrounding their test results.
For example, say you're following up with a patient in your buprenorphine program and their UDT suggests that they may be having some challenges taking the medication. You might say something like, "Your urine test was negative for buprenorphine and positive for fentanyl. Was this expected for you?" Then let them engage in the dialogue and go from there.
What different types of UDTs are available?
Stahl: Generally, there are two types of UDTs: screening Immunoassays (which use antibody technology) and confirmatory testing (uses gas or liquid chromatography paired with mass spectrometry).
The screening immunoassays test for common panel substances - a standard panel for a given institution - and results can be obtained quickly. The screening tests are cheap, so this is what we will encounter most often in the clinical setting, but we have to be cautious in interpreting them. They are screening tests; they are not perfect. Other substances can cross-react with antibodies, producing false positives. False negatives can occur also.
Since these test results can have a big influence on management or other consequences down the road, we must be mindful of potential false positives and the implications. Common medications that can cause false positives for amphetamine in a screening UDT, for example, include bupropion, pseudoephedrine, and over-the-counter Vicks decongestant (which contains l-methamphetamine). So, technically, it's a true positive, but it's not the illicit amphetamines that we might be looking for.
A common medication that can cause a false positive for benzodiazepine is sertraline, which is often used to treat anxiety. Medications that can cause positive phencyclidine results include dextromethorphan, carbamazepine, tricyclic antidepressants, and venlafaxine.
If you want to avoid a false positive, confirmatory testing is often accessible, but it's more expensive and it takes longer to get results back. Will it impact patient care or change your management? Is this a high-stakes legal scenario, such as a patient involved with child protective services or on probation? In situations where it might affect their lives to have a false positive, think about doing confirmatory testing.
What were some of the pearls on interpreting opiate and opioid UDT results?
Chan: With the opioid overdose crisis, physicians prescribing opioids for pain or treating opioid use disorder often use UDTs to monitor adherence or progress. But it's important to interpret these results carefully because it's not always straightforward. And in my practice, I honestly find this to be one of the more challenging tests to interpret.
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