Evaluation of the AxSYM monoclonal cyclosporin assay and comparison with radioimmunoassay

Recently, a semiautomated fluorescence polarization immunoassay (FPIA) for determination of parent cyclosporin (CsA) has been developed for the Abbott AxSYM system. The new CsA assay measures the drug from an extracted whole blood specimen. The authors report here the evaluation of this new assay an d the comparison with a previously validated radioimmunoassay (RW) method ( CYCLO-Trac SP). To assess the imprecision, the authors used tri-level contr ols supplied by both Abbott and Bio-Rad manufacturers. The within-run CV ra nged from 4.4% to 7.3% and the between-day CV ranged from 4.4% to 7.6%. Mea n recovery of the drug from clinical specimens spiked with kit calibrators was 108.4%. Fluorescence polarization immunoassay AxSYM (y) was correlated to RLA (x) by using 132 trough blood specimens (44 renal, 44 liver, and 34 heart) from transplant recipients and resulted in the following Passin-Babl ok linear regression equation: y = 6.7 + 0.97x, r = 0.989, S-x/y = 12.9. Th e percentage of overestimation (mean, range) by FPIA AxSYM versus RIA was ( 3.8%, range -17.7% to 39.1%). The results observed with this new method fro m follow-up studies in patients during the early course after transplant we re not consistently higher than those obtained by RIA. These findings contr ast with previously reported results that compared FPIA TDx assay with RIA. The authors conclude that FPIA AxSYM is a precise method for measuring CsA and offers results similar to those obtained by RIA with a marked reductio n in assay time.