Evaluation of the TDx method for cyclosporine and a comparison to CYCLO-Trac RIA in renal transplant patients.

The recent introduction of a fluorescence polarization immunoassay (FPIA) for cyclosporine by Abbott for their TDx analyzer provides an alternative to radioimmunoassay (RIA) and high performance liquid chromatography procedures. This new method is easier and faster than the Incstar CYCLO-Trac RIA assay. The TDx method has good precision except at low levels of cyclosporine. RIA gives consistently higher values than FPIA for samples containing only cyclosporine and in those from renal transplant patients. The FPIA procedure may be modified to allow up to a 50-min pause during the protein precipitation step, allowing more efficient use of technologists' time.