Comparison of ELISAs for Opiates, Methamphetamine, Cocaine Metabolite, Benzodiazepines, Phencyclidine, and Cannabinoids in Whole Blood and Urine

Abstract

ELISAs are widely utilized in forensic drug analysis. A comparative assessment of microtiter plate assays for the detection of six common classes of drug in blood and urine is described. ELISAs for opiates, methamphetamine, benzodiazepines, cocaine metabolite, phencyclidine (PCP), and tetrahydrocannabinol (THC) metabolite were evaluated in a side-by-side study. The analytical performance of 12 commercially available ELISAs was determined in terms of binding characteristics, dose-response curves, limits of detection, sensitivity, intra- and interassay imprecision, and lot-to-lot reproducibility. Assay performance was also compared using 855 forensic casework samples. Detection limits in whole blood for morphine, D-methamphetamine, nordiazepam, benzoylecgonine, nordiazepam, PCP, and L-11-nor-9-carboxy-delta9-THC were 3, 2, <4, 5, 25, and 3 microg/L, respectively, for the STC ELISAs. Corresponding detection limits for Immunalysis ELISAs were <1, <2, <4, 5, <1, and 1 microg/L, respectively. Intraassay CVs (n = 8) at the immunoassay cutoff concentrations were 4.1-5.6% and 3.5-11% for STC and Immunalysis ELISAs, respectively. Corresponding interassay CVs were 3.1-10% and 6.5-20%. Of the 855 casework samples, there were a total of 92 discordant results (44 cannabinoid, 15 opiate, 15 methamphetamine, 11 benzodiazepine, and 7 cocaine metabolite). Gas chromatography-mass spectrometry analysis indicated a total of three unconfirmed positive results for Immunalysis assays and one unconfirmed positive for STC assays. A comparative assessment of drugs-of-abuse assays from two manufacturers indicated some key differences in analytical performance. Overall, Immunalysis assays offered superior binding characteristics and detection limits, whereas STC assays offered improved overall precision and lot-to-lot reproducibility.