Comparison of Abbott TDx fluorescence polarization immunoassay, Sandoz radioimmunoassay, and high-performance liquid chromatography methods for the assay of serum cyclosporine.

: We have had the opportunity to compare the new FPIA method for the measurement of serum Cs to established assays. The technique used a precipitation step prior to the fluorescence polarization measurement. We compared serum HPLC and RIA to the FPIA procedure. The within run coefficients of variation were 7.2%, 9.5%, and 4%, respectively. Between run CVs were 8.0%, 12.2%, and 3.8%. The correlation coefficient for HPLC and both of the immunoassays was less than 70%, showing the influence of the different specificities of the techniques. Medical centers that have based patient care on the HPLC assay that measures only parent drug will have difficulty using an immunoassay that measures a combination of parent and metabolites. There was a good correlation (R2 = 0.93) between the two immunoassays indicating that those currently using the serum RIA for monitoring could, through careful correlation studies in their patient population, use the FPIA technique. The regression equation was as follows: serum FPIA = 1.27 serum RIA + 1.9. This indicates the higher bias of the FPIA measurements. The advantages of the FPIA assay are that 20 assays could be done in less than one hour. This is in contrast to the longer turnaround time of the standard Sandoz RIA procedure. The technical competence required to perform the assay is less than that needed to perform the current RIA procedure. The assay can be recommended for replacement of the serum RIA; however, a correlation of levels with clinical experience is necessary in view of the difference in values between RIA and FPIA.