Three commercial polyclonal immunoassays for cyclosporine in whole blood compared: 1. Results with patients' specimens.

We assessed the performance of three commercially available polyclonal immunoassays for apparent cyclosporine in 120 whole-blood specimens collected from transplant recipients just before their next dose of cyclosporine (CsA). The assays were (a) Abbott's TDx fluorescent polarization immunoassay for CsA and its metabolites in whole blood; (b) the Sandoz radioimmunoassay (RIA); and (c) Incstar's Cyclo-Trac RIA. Mean respective CVs were 3.8%, 9.3%, and 24.3%. Analytical recovery was nearly 100% for concentrations up to 1000 micrograms/L for Incstar and up to 1500 micrograms/L for Abbott and Sandoz; linearity was compromised at greater concentrations. We also quantified the parent CsA concentrations by HPLC. Moreover, to follow day-to-day fluctuations in patients' "cyclosporine" concentrations with each method and to assess the impact these differences have on interpretation of the analytical results, we assayed serial specimens from six post-transplant patients. These showed significantly dissimilar, but parallel, results among the methods for any single sample. Occasionally, however, a result would not fit the established trend. Biases observed among the assays can be explained in part by the nonspecific antisera cross-reacting with CsA metabolites. Most important, we demonstrate that patients' results are not reliably interchangeable among the methods.