Nonselective measurement of cyclosporine for therapeutic drug monitoring by fluorescence polarization immunoassay with a rabbit polyclonal antibody: I. Evaluation of the serum methodology and comparison with a sheep polyclonal antibody in an 3H-tracer mediated radioimmunoassay.

Among the new techniques available for CyA monitoring, the FPIA offers the advantages of rapidity and simplicity. The present communication assesses the technical performance of this test in comparison with a 3H tracer-based PC-RIA for serum CyA levels using 971 samples obtained during the first 6 posttransplant months from 14 kidney transplant recipients. The FPIA evaluation included verification of CyA concentrations in manufacturer-supplied calibrators and controls by reference methods, determination of intraassay/interassay precision and accuracy, feasibility of specimen dilution and assessed assay sensitivity, and range of linearity. Comparison of FPIA with PC-RIA indicated that trough samples, when assessed by FPIA, averaged 1.3-fold greater than the PC-RIA, whereas non-trough FPIA measurements indicated similarity between the two methods. Although the two assays showed similar trends in most renal transplant recipients, two subjects demonstrated discrepancies, presumably reflecting the differing specificities of the polyclonal antibodies used in each assay. Thus, the FPIA appears to be a useful addition to CyA monitoring technology.