An evaluation of the cyclosporine parent-compound-specific whole blood TDx assay

The new Abbott TDx cyclosporine parent-compound-specific fluorescence polarization immunoassay (TDxP) was evaluated and compared to the cyclosporine-and-metabolites-specific TDx (TDxT) and a cyclosporine parent-compound-specific radioimmunoassay (RIA) (Sandimmun-Kit, INCSTAR). The TDxP assay was linear within the range of 31 to 1600 ng/ml (r = 0.985) with a lower limit of detection of less than 31 ng/ml. The TDxP had excellent intra- and interassay reproducibility (CV = 1.2 to 4.5) that was significantly better than that of the radioimmunoassay. 230 whole blood samples obtained from 65 kidney, 19 liver, and 8 pancreas transplant recipients were analyzed with each of the three assay methods. TDxP had a much stronger correlation with the RIA than did TDxT (r = 0.95 versus 0.83). The difference between the correlations was greatest for the liver and pancreas recipients. The mean ratio of the cyclosporine level determined by TDxP to RIA was 1.0 versus 2.4 for TDxT to RIA. The new TDxP assay provides results equal to a parent-compound-specific RIA but with the added advantages of decreased sample turn-around time and improved intra- and interassay coefficients of variation.