RESUMO
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.
