Comparison of the Serum Barbiturate Fluorescence Polarization Immunoassay by the COBAS INTEGRA to a GC/MS Method

The authors evaluated a new Cassette Serum Barbiturates fluorescence polarization immunoassay (FPIA) on the COBAS INTEGRA. The assay was calibrated with secobarbital standards at 0, 0.5, and 4.0 microg/mL. The assay range was 0.030 to 80 microg/mL using an automatic 1/20 postdilution feature. Precision was established for two COBAS INTEGRA instruments for ten days by assaying secobarbital target concentrations ranging from 0.125 to 2.2 microg/mL. The coefficients of variation (CV) for the above target concentrations for the first instrument ranged from 2.7% to 8.3%, and for a second instrument, 3.8 to 8.3%. Seven clinically elevated bilirubin samples were spiked with 0.46 and 1.77 microg/mL secobarbital. Bilirubin interference was less than 10.9 and less than 7.9%, respectively. The average recovery ranged from 85% to 94%. The mean difference in recovery in serum versus plasma was < or = 3%. Fifty-two clinical samples were analyzed for butalbital, pentobarbital, secobarbital, and phenobarbital by GC/MS, and the results were compared to the new Cassette Serum Barbiturates FPIA. The diagnostic sensitivity and specificity were 95% and 100%, respectively. Both FPIA and GC/MS assays are clinically efficacious for monitoring serum barbiturates.