Nonfatal tramadol overdose may cause false-positive phencyclidine on Emit-II assay

Abstract

False-positive results are a common finding with qualitative urine drug screens. This report describes 2 patients with positive phencyclidine (PCP) screens using the Emit II Plus Drugs-of-Abuse Test (Siemens Healthcare Diagnostics, Inc, Tarrytown, NY) after tramadol ingestion. Our first case was a 43-year-old woman with a history of bipolar disorder who presented to the emergency department(ED) for medical clearance after ingesting an unknown amount of tramadol. Her urine drugs-of-abuse screen was positive for PCP. A comprehensive gas chromatography/mass spectrometry qualitative urine drug screen demonstrated valproic acid metabolites, nicotine, gabapentin, benztropine, and a large peak of tramadol. Our second case was a 3-year-old boy with a medical history of previous ingestions presented to the ED for altered mental status and suspected ingestion. His urine drugs-of-abuse screen was positive for PCP. A comprehensive gas chromatography/mass spectrometry qualitative urine drug screen demonstrated a large peak of tramadol. Molecular similarity analysis can predict cross-reactivity of drug of abuse and therapeutic drug monitoring assays. This computational analysis demonstrated that tramadol and its metabolite possess enough similarity to PCP to produce positives due to interaction with the assay antibody (or antibodies). Tramadol and its metabolites can cause a false-positive Emit II+ PCP screen, and clinicians should use caution when interpreting urine drugs-of-abuse screens that use immunoassays.