False-positive levorphanol (opioid) due to dextromethorphan on urine drug screen by time-of-flight MS

A case of a false-positive levorphanol on an LC-QTOF urine drug screen due to the presence of dextromethorphan is described. Levorphanol is a stereoisomer of dextrorphan, the main metabolite of dextromethorphan. Dextromethorphan does not produce the same analgesic and sedative effects as opioids, which exhibit nervous system and respiratory depression. LC-MS assays are not able to distinguish between stereoisomers, and thus dextrorphan in the sample will be recognized as levorphanol. Only enantiomeric chiral LC-MS/MS analysis can help differentiate the two compounds. The primary caregiver was notified that with dextromethorphan present, the detected levorphanol was most likely the metabolite dextrorphan.