False-Positive Urine Drug Screens

2016-04-02T14:50:10Z

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from ClinicalPearl@EMedHome.com, http://www.emedhome.com

Enzyme immunoassay qualitative techniques for urine toxicology screening are commonly used because of their wide availability, lower cost and reduced testing time compared with nonimmunologic techniques. Commonly used medications can interact with immunoassay urine tests and result in false-positive results.

If a urine drug screen result is suspected of being falsely positive, confirmatory testing with a nonimmunologic, quantitative technique (e.g. mass spectroscopy) should be performed.

{| border="1" style="border-collapse:collapse" cellpadding="5"
|+Cross-reactivity of commonly used medications in urine screening assays (1,2)
|- style="text-align:left;"
! Drug identified in false-positive result
! Medication responsible for result

|-
|Opiate
|Levofloxacin, ofloxacin, rifampin

|-
|Amphetamine
|Bupropion, ephedrine, Vicks Vapor Inhaler
|-
|Barbiturate
|Ibuprofen, naproxen

|-
|Phencyclidine
|Venlafaxine, tramadol
|-
|Benzodiazepines
|Efavirenz (an HIV antiviral)
|-
|Methadone
|Quetiapine (Seroquel)
|}

References:
(1) Tobin DG, et al. CCJM 2016 Mar;83(3):207-215.
(2) Saitman A, et al. J Anal Toxicol 2014;38(7):387-96.

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False-Positive Urine Drug Screens