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Published:
Journal of Analytical Toxicology,
ISSN 0146-4760,
Volume 27, Number 8, November/December,
pp. 587-591
TECHNICAL NOTE: Performance of a Microtiter Plate ELISA
for Screening of Postmortem Blood for Cocaine and Metabolites
Vina Spiehler[1], Daniel S. Isenschmid[2], Parrish
Matthews[3],
Philip Kemp[4],
and Tom Kupiec[3]
[1]Spiehler & Associates, Newport Beach, California;
[2]Office of the Wayne
County Medical Examiner, Detroit, Michigan;
[3]Analytical Research Laboratories,
Inc.,
Oklahoma City, Oklahoma; and
[4]Office of the Medical Examiner, Oklahoma City,
Oklahoma
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). Reproduction
of editorial content of this journal is prohibited without publisher’s
permission.
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