Performance of a Microtiter Plate ELISA for Screening of Postmortem Blood for Cocaine and Metabolites

Abstract

The object of this study was to evaluate the suitability of the Neogen Corporation microtiter plate enzyme-linked immunoassay (ELISA) for cocaine and metabolites for screening of postmortem blood. Sixty-five postmortem whole blood specimens were obtained from drug-involved deaths that had been screened and confirmed positive for cocaine and/or benzoylecgonine (BE). Fifty-eight negative specimens were obtained from noncocaine-involved deaths. Specimens were tested using the Neogen™ Cocaine/BE microtiter plate ELISA assay. No matrix effects were found for whole blood in this assay. The effect of dilutions of the whole blood specimens of 1:5 through 1:50 was studied. A dilution of 1:5 was chosen to correspond to that used for other Neogen microtiter plate assays for drugs in whole blood. True positives, true negatives, false positives, and false negatives were determined and graphed for the ELISA results against gas chromatography-mass spectrometry (GC-MS), GC-nitrogen-phosphorus detection, and case histories. From these graphs and the receiver operating characteristic curves, the optimal cutoff for the Neogen Cocaine/BE ELISA was found to be 5 ng/mL BE equivalents at a 1:5 dilution. The optimum cutoff for a 1:50 dilution was 50 ng/mL BE equivalents. The Neogen Cocaine/BE ELISA had a sensitivity of 93.8% ± 2.9% and a specificity of 96.6% ± 2.4% versus GC-MS at a cutoff of 5 ng/mL BE equivalents (1:5 dilution) and a sensitivity of 100% ± 0.5% and specificity of 98.3% ± 1.7% versus GC-MS at a 50 ng/mL BE equivalents cutoff (1:50 dilution).