Evaluation of the Abbott TDx for determination of phenobarbital in forensic blood specimens

The Abbott TDx was evaluated for determination of phenobarbital (PB) levels in postmortem (PM) blood. Because hemolysis does not interfere with fluorescence polarization assays, the TDx could be a fast, efficient alternative to gas chromatography (GC). The linearity and precision of the TDx assay were evaluated using postmortem blood that was spiked with phenobarbital and serially diluted. The relationship between nominal and measured values was linear for phenobarbital concentrations up to 150 mg/L (r = 0.999) in two separate postmortem bloods. Precision was excellent with run-to-run coefficients of variation of 10% or less. The TDx results for phenobarbital in spiked PM blood were compared to those determined by GC. An excellent correlation (r = 0.999) between the TDx results and GC results was achieved. PM blood specimens from ten forensic cases were assayed for PB by GC and compared with PB results from the TDx. Comparison of these results also showed good correlation (r = 0.959). These data indicate that the Abbott TDx can be used reliably in the estimation of PB levels in postmortem whole blood samples.