Preliminary evaluation of the Abbott TDx for screening of D-methamphetamine in whole blood specimens

The Abbott TDx Urine Amphetamine/Methamphetamine II fluorescence polarization immunoassay technique was applied to the determination of D-methamphetamine in hemolyzed whole blood. The assay was found to have 100% cross-reactivity with D-methamphetamine and only an 8% cross-reactivity with L-methamphetamine. Whole blood was fortified with D-methamphetamine at concentrations ranging from 25 to 1000 ng/mL. These whole blood calibrators were used to evaluate the following sample preparation techniques: direct, diluted and buffer, and precipitated using methanol, acetone, sulfosalicylic acid, trichloroacetic acid, and zinc sulfate. Calibrators and samples were prepared by mixing 200 microL of whole blood and 200 microL precipitation reagent and centrifuging at 10,000 rpm for 5 min (9600 x g). A 50-microL aliquot of the supernatant was used for the assay. Using the zinc sulfate precipitation, blood calibration curves showed a linear range of 25-1000 ng/mL. The within-run precision for the 25-, 60-, and 200-ng/mL D-methamphetamine blood controls showed percent coefficients of variation of 17.8, 17.0, and 5.4, respectively. The TDx results were compared to RIA and GC/MS assays for the methamphetamine controls and for eight positive case specimens and found reliable for the screening of hemolyzed whole blood.