|SOFT - TIAFT 1998||Poster Session 2||Wednesday October 7, 1998|
USE OF THE IMMULITE® CHEMILUMINESCENCE IMMUNOASSAY SYSTEM FOR THE SCREENING OF POST-MORTEM AND DUID BLOOD SPECIMENS|
Joseph J. Saady, B. Douglas McIntosh, Jr. and James Valentour
Virginia Division of Forensic Science, 700 N. 5th St, Richmond, VA 23219, USA
The Diagnostic Products Corporation IMMULITE benchtop random-access immunoassay analyzer was evaluated in our laboratory. This system uses enzyme-amplified chemiluminescence and centrifugal separation of reactants. Untreated post-mortem blood specimens or Driving Under The Influence Of Drugs (DUID) blood specimens were placed directly into the instrument sampling cup. The performance of kits designated as opiates (OPI), benzoylecgonine (BE), and tetrahydrocannabinol carboxylic acid (THCA) were compared to the corresponding Abbott TDx kit methodology. Specimens testing positive by IMMULITE and/or TDx were submitted for confirmation and quantitation by gas chromatography/mass spectrometry (GC/MS).
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.