NONINTERCHANGEABILITY OF SPECIFIC RADIOIMMUNOASSAY AND MONOCLONAL-ANTIBODY FLUORESCENT POLARIZATION IMMUNOASSAY IN CYCLOSPORINE MEASUREMENTS

This study compares cyclosporine (CsA) concentrations in whole blood f rom patients receiving bone marrow (n = 10), renal (n = 48), heart (n = 50) or liver (n = 50) transplants, as measured by monoclonal antibod y flurorescence polarization immunoassay (FPIA) and specific I-125-rad ioimmunoassay (RIA). The FPIA overestimated CsA by an average of 25%. Results were higher for all indications: FPIA/RIA ratios were 1.17 for bone marrow, 1.23 for renal and 1.27 for both heart and liver transpl ants, and these values were significantly different from 1.0. The perc entage of overestimation was higher at low CsA concentrations (less th an or equal to 100 mu g/L) than at high CsA concentrations (greater th an or equal to 400 mu g/L). In all indications, results by both method s correlated well (r > 0.96) but slopes and intercepts were different from 1.0 and 0.0, respectively, and these parameters varied greatly be tween the grafted populations. These findings obtained with the two me thods could nor be attributed to matrix effect because the mean FPIA/R IA ratio for spiked control samples was 1.0. The discrepancy between t he FPIA and RIA could be explained by the lower specificity of the mon oclonal antibody contained in the FPIA kit. These results suggest that FPIA is not as accurate as RIA and that the two methods are not inter changeable in CsA level measurement.