Virginia Division of Forensic Science, 700 N. 5th St, Richmond, VA 23219, USA

IMMULITE methodology required no sample preparation while the TDx required a buffer dilution for OPI and BE, and an acetonitrile extraction for THCA. Both methodologies produced the same results for COC with 15 positive and 44 negative specimens (n = 59). GC/MS confirmed the accuracy of all positives. OPI comparisons (n = 61) produced 14 positives and 47 negatives for both techniques, however, GC/MS confirmed 2 false positives (FP) and 1 false negative (FN) by TDx vs. 1 FP by IMMULITE. THCA testing produced 23 and 22 positives and 29 and 32 negatives by IMMULITE and TDx, respectively. GC/MS confirmed 2 FN by TDx and 1 FN by IMMULITE.

Precision studies using three varying concentrations of unaltered postmortem blood for each analyte were conducted (n = 10 or 11), and morphine precision was found to range from 8.1% to 10.8%, BE from 5.5% to 33.7%, and THCA from 3.2% to 13.2%. Cross-reactivity studies were performed with approximately 70 drugs at blood concentrations ranging from 5000 to 10,000 ng/mL and showed less than 2% cross-reactivity.

The IMMULITE was found to produce reliable screening results with less inaccuracies than TDx. Furthermore, postmortem blood and DUID blood specimens required no specimen pretreatment.