False-positive reports on urine drug screens by immunoassay are rare (strength of recommendation [SOR]: C, small controlled-exposure studies, small case series). Nonsteroidal anti-inflammatory drugs, fluoroquinolones, and Vicks Inhaler are most frequently implicated (TABLE). Ruling out a false-positive result requires confirmation with a more specific test, usually gas chromatography/mass spectrometry (GC-MS). A true-positive drug screen may occur in a urine specimen from a patient who legally or unknowingly ingests a product that is metabolized to a drug of abuse. Passive exposure to a substance is unlikely to cause a positive drug screen (SOR: B, small controlled-exposure studies)
