Emergency department evaluation of a rapid assay for detection of cocaine metabolites in urine specimens

We evaluated the Abuscreen ONTRAK assay for cocaine metabolites, a rapid immunoassay for the detection of cocaine metabolites in a pediatric emergency department (ED) setting. The ONTRAK uses a cutoff point of 300 μg/L for benzoylecgonine (BEC), cocaine's major urinary metabolite. One hundred and thirty-two urine specimens obtained from infants, children, and adolescents whose clinical findings warranted toxicology screening were evaluated. The ONTRAK identified all 15 specimens with BEC values of 300 μg/L, but did not detect seven additional specimens positive for cocaine metabolites at concentrations less than 300 μg/L. One third of the positive specimens for cocaine metabolite identified by fluorescent polarization immunoassay (FPIA), cutoff point set at 80 μg/L, and confirmed by gas chromatography/mass spectrometry (GC/MS), cutoff point 50 μg/L, were not detected by the ONTRAK. These false negative specimens were seen exclusively in young children, whose concentration of cocaine metabolite was less than the ONTRAK's cutoff value. The test was sensitive to drug concentration at or around the stated cutoff values. The ONTRAK test for cocaine metabolites, although both a sensitive and specific screening test for adolescents who smoke or snort cocaine, lacks the sensitivity to be a useful screening tool for detecting cocaine metabolites in young children. Limitations of currently performed toxicology screening tests (ie, stated cutoff levels) may cause emergency physicians to miss most young children whose symptoms may be related to cocaine exposure.