Monoclonal antibody fluorescent polarisation immunoassay versus 125Iode labelled ligand radioimmunoassay for the measurement of cyclosporine concentrations in whole blood

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Abstract
Monoclonal antibody fluorescent polarisation immunoassay for cyclosporine in whole blood was first evaluated. Inter- and intra-assay CVs were less than 7%. We also compared concentrations measured by 125I-RIA and FPIA in specimens obtained from kidney and bone marrow transplanted patients. FPIA correlated well with 125I-RIA (slope = 1.03, r = 0.989, n = 58) over a wide range of concentrations (44-984 ng/ml). However, an additive bias estimated by the mean difference in cyclosporine concentrations between the 2 readings (44.1 +/- 44.3 ng/ml), led to overestimation of cyclosporine concentrations measured by FPIA. The monoclonal FPIA kit is therefore a rapid and reproductive method to monitor cyclosporine concentrations in whole blood. However, FPIA and 125I-RIA are not interchangeable and the therapeutic range of cyclosporine measured by FPIA should be defined.