Evaluation and comparison of therapeutic monitoring of whole-blood levels of cyclosporin A and its metabolites in renal transplantation by HPLC and RIA methods

Background: The aim of the work was to evaluate the possibility to estimate the level of cyclosporin A (CyA) metabolites as the difference of radioimmunoassay (RIA) non-specific and RIA specific methods. Methods: Blood samples of renal transplant patients were analyzed by three different methods: RIA specific method (CYCLO-Trac, DiaSorin, USA) (RIA_SP), RIA non-specific method (Immunotech, Czech Republic) (RIA_NS), and high performance liquid chromatography (HPLC) method. Results: Although values obtained by RIA_SP correlated well those obtained by HPLC (RIA_SP=0.995·HPLC+9.68; r²=0.962, n=448), the results of HPLC methods were lower by 8%. The values obtained by RIA_NS were 2.57 times higher than the values obtained by RIA_SP (RIA_SP=0.356RIA_NS; r²=0.713, n=448). The ratio (CyA+CyA metabolites)/(CyA) calculated as the ratio RIA_NS/RIA_SP values for 42 renal transplant patients was relatively stable for each particular patient. The sum of selected CyA metabolites (M1+M17+M21) measured by HPLC correlated well with that estimated from the difference of RIA_NS−RIA_SP: HPLC_metab=0.921·(RIA_NS−RIA_SP)+21.3; (r²=0.746, n=448). Conclusion: The combination of both the specific and non-specific methods for the determination of CyA presents an improved means for the TDM of CyA and CyA metabolites in renal transplant patients. Moreover, a combination of both methods can help to elucidate some unexpected events, such as the persistence of high cyclosporin blood levels.