Determination of blood sirolimus concentrations in liver and kidney transplant recipients using the Innofluor® fluorescence polarization immunoassay: Comparison with the microparticle enzyme immunoassay and high-performance liquid chromatography-ultraviolet method

Background. Although high-performance liquid chromatography (HPLC) is the method of choice for blood sirolimus determination, the microparticle enzyme immunoassay (MEIA) run on the IMx® analyser is widely used in therapeutic monitoring of this immunosuppressant agent. The aim of our study was to evaluate the possible determination of sirolimus using the fluorescence polarization immunoassay (FPIA) commercialized for everolimus quantification.Methods. Sirolimus concentrations were determined in whole-blood samples from liver and kidney transplant recipients using the Innofluor® Certican® FPIA (Seradyn Inc.) run on a TDx® analyser (Abbott Laboratories), Sirolimus MEIA run on an IMx® analyser (Abbott Laboratories), and HPLC (UV detection) methods.Results. The Innofluor® FPIA has a similar cross-reactivity with everolimus and sirolimus, and the within- and between-run coefficients of variation obtained for sirolimus determination were 2.7%–13.3%. In analysing different blood samples from liver and kidney tran...