Validation of an automated microplate enzyme immunoassay for screening of postmortem blood for drugs of abuse.

The objective of this study was to compare the sensitivity and specificity of an enzyme immunoassay employing antibodies bound to a microtiter plate (MPEIA) with those of two radioimmunoassays for screening postmortem blood from selected coroner's cases for drugs of abuse. The radioimmunoassays were a coated-tube radioimmunoassay (CTRIA) and a double antibody radioimmunoassay (DARIA). Specimens consisted of 260 postmortem blood specimens from coroner's cases. Immunoassay results (positive or negative) were compared with confirmed results on those cases by gas chromatography-mass spectrometry, alone or in combination with gas-liquid chromatography using either a nitrogen-phosphorus or flame-ionization detector. Sensitivity was calculated as the true-positive rate using chromatographic confirmation as the reference standard. Specificity was calculated as the true-negative rate. Sensitivity and specificity were calculated for 5-7 potential cutoff concentrations for the drug classes opiates, amphetamines, cocaine and metabolites, and barbiturates. For opiates, the sensitivity and specificity were 99% and 93%, respectively, for the MPEIA at a cutoff of 20-ng/mL morphine, compared with 94% and 96% for the CTRIA at a cutoff of 5-ng/mL morphine and > 99% and 96% for the DARIA at 20-ng/mL morphine. For cocaine and metabolites, the sensitivity and specificity were 96% and 93%, respectively, for the MPEIA at 50-ng/mL benzoylecgonine, compared with 93% and 96% for CTRIA at 50-ng/mL benzoylecgonine and 98% and 97% for the DARIA at 50-ng/mL benzoylecgonine. For amphetamines, the sensitivity and specificity were >99% and 91%, respectively, for the MPEIA at 25-ng/mL methamphetamine, compared with 93% and 86% for the CTRIA at 25-ng/mL methamphetamine and 83% and 89% for the DARIA at 50-ng/mL methamphetamine. For barbiturates, the sensitivity and specificity were > 99% and 92%, respectively, for the MPEIA at 50-ng/mL secobarbital, compared with 91% and 87% for the CTRIA at 500-ng/mL secobarbital and 79% and 95% for the DARIA at a cutoff of 1000-ng/mL phenobarbital.

Setting cutoff concentrations for immunoassay screening of postmortem blood.

The objective of this study was to establish the optimum immunoassay cutoff concentrations for screening postmortem blood from coroner's cases for drugs of abuse with a coated tube radioimmunoassay (RIA) to ensure that the results with the coated tube RIA would be equal to or better than those with the previously used double antibody RIA. Immunoassay results (positive or negative) blood were compared to confirmed results on those cases by GC/MS alone or in combination with GLC using either a NPD or FID detector. Four to seven potential cutoff concentrations were evaluated for the drug classes opiates, amphetamines, cocaine and metabolites, and barbiturates. Specimens were 350 postmortem blood specimens and liver homogenates. The cutoffs chosen for the coated tube RIA using this approach were 5 ng/mL morphine, 25 ng/mL methamphetamine, 500 ng/mL benzoylecgonine, and 500 ng/mL secobarbital. These cutoffs corresponded to a sensitivity and specificity of 94% and 96% for opiates, 93% and 86% for amphetamines, 91% and 96% for cocaine and metabolites and 91% and 87% for barbiturates. The double antibody RIAs were run on the same specimens with cutoffs of 20 ng/mL morphine, 50 ng/mL methamphetamine, 50 ng/mL benzoylecgonine and 1000 ng/mL phenobarbital. The sensitivity and specificity's for the double antibody immunoassay were: > 99% and 96% for opiates, 83% and 89% for amphetamines, 98% and 97% for cocaine, 79% and 95% for barbiturates.

Toxicologic data from documented drug-induced or drug-related fatal cases.

Seventy-six fatal cases are presented in which the total dose of drug(s) ingested is known. Blood and liver concentrations for the various drugs are given, as well as the total recovery from the stomach contents.