CYCLOSPORINE-A MONITORING IN PATIENTS WITH RENAL, CARDIAC, AND LIVER-TRANSPLANTS - A COMPARISON BETWEEN FLUORESCENCE POLARIZATION IMMUNOASSAY AND 2 DIFFERENT RIA METHODS

In the present study a new method for selectively determining parent c yclosporine (CsA) in whole blood, a fluorescence polarization immunoas say (FPIA; TDx Abbott), was compared with a RIA method (Sandimmun, San doz Ltd, Basle, Switzerland). A total of 974 samples were collected du ring the first 3 post-operative months from 63 renal, cardiac, and liv er transplant recipients. The CsA concentrations measured with FPIA ra nged from 14% to 19% above RIA (specific) in the middle ranges. Regres sion equations in renal transplants: FPIA = 1.001 x RIA + 28; in heart transplants: FPIA = 1.08 x RIA + 27 and in liver transplants: FPIA = 1.13 x RIA + 13. Considering the improved precision of the new method (inter-assay CV with FPIA: 3.8-9.5%; with RIA: 18.6%), the slightly lo wer specificity will usually be of minor importance in the therapeutic range for whole blood CsA concentrations following organ transplantat ions. The FPIA measurements which deviated most from the regression li ne compared with RIA-specific CsA values, tended to coincide with high CsA concentrations or rather extreme RIA specific to RIA non-specific ratios. In addition to analytical imprecision with the RIA-specific m ethod, lower specificity of the FPIA vs. some of the metabolites may e xplain these deviations. The majority of these observations occurred a s isolated episodes with normal relationship between RIA specific and FPIA on preceding and following days. Accordingly large dosage adjustm ents should await verification in repeated samples. Following these pr ecautions the FPIA method may prove useful and safe in the monitoring of cyclosporine treatment.