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To the Editor: We report the case of an unexpected positive result on routine urine drug screening for phencyclidine in a patient who assured that she had never used such substance. Because similar results have recently been reported (1, 2) and in order to avoid inappropriate suspicion by medical caregivers, we performed a blood test that confirmed the absence of phencyclidine and the interpretation of the former urine test as a false positive result.

“Ms. A,” a 48-year-old patient with a 31-year history of recurrent depressive disorder, was admitted to the psychiatric hospitalization unit for an acute exacerbation of her mental disorder. She was receiving treatment with venlafaxine 225 mg/day, lamotrigine 100 mg/day, and lormetazepam 2 mg/day. During the prior month she experienced worsening of the depressive symptoms, concurrent with mood-incongruent psychotic symptoms that were not of a clearly depressive …