False-Negative Result for Cocaine Metabolites on a Lateral-Flow Drug Test Slide Corrected by Dilution

Cocaine is one of the most widespread drugs of abuse; therefore, clinical laboratories are frequently requested to screen for the presence of cocaine and its metabolites in urine. When screening a urine specimen from a potential study participant for drugs of abuse, using a Verdict™ II lateral flow test slide (MEDTOX™ Diagnostics), multiple technologists obtained a negative screening result for benzoylecgonine (BE) on repeat analysis (n = 25). Because the study participant did not show symptoms of cocaine toxicity despite admitting to cocaine use and because the Verdict II drug test slide gave a negative result, the urine specimen was sent to Mayo Medical Laboratory (Rochester, MN) for a comprehensive drug screen and confirmation of cocaine and its metabolites by gas chromatography-mass spectrometry (Model 5973; Agilent™ Technologies) using solid-phase extraction and trimethylsilyl derivatization, as described by Chinn et al. (1). Gas chromatographic-mass spectrometric testing indicated that the urine …