Evaluation of immunoassay methods for the screening of cocaine metabolites in urine

Immunoassay kits for urine cocaine (and metabolite) screening, obtained from two commercial sources, were examined for correlation of their results, expressed in terms of equivalent benzoylecgonine concentration, with the gas chromatography/mass spectrometry (GC/MS) concentration of benzoylecgonine. The correlation coefficients obtained, based on 62 (out of a total sample population of 3295) highly relevant samples, were 0.467 and 0.766 for Abuscreen (ARIA) and TDx (TDX), respectively. The preliminary screen cutoff values, which correspond to 150 ng/mL benzoylecgonine (as determined by GC/MS), were calculated based on the resulting regression equations and found to be 380 and 190 ng/mL for ARIA and TDX, respectively. With these cutoff values, ARIA generates 5 false negatives and 16 unconfirmed presumptive positives, while TDX results in 3 false negatives and 6 unconfirmed presumptive positives.