Three Commercial Polyclonal Immunoassays for Cyclosporine in Whole Blood Compared: 2. Cross-Reactivity of the Antisera with Cyclosporine Metabolites

We demonstrate the diverse selectivity of three commercial polyclonal “cyclosporine ” immunoassays for cyclosporin (CsA) metabolites by comparing analytical responses of nine metabolites added to drug-free whole-blood specimens (range 0 to 2000 pg/L) and assayed by the Abbott TDx fluorescence polarization immunoassay (FPIA), the Incstar Cyclo-Trac radioimmunoassay (AlA), and the Sandoz AlA. Cross-reactivity--defined as the relative response (slope of regression line) of metabolite/parent CsA over the assay’s linear range of concentrations-differed for each metabolite among the three assays. Overall, Abbott’s antiserum exhib-ited the greatest affinity for the metabolites, the Sandoz antiserum the least. Ranges of cross-reactivity for the metab-olites over all three assays were Ml (14-44%), M8 (9-20%)