Evaluation of a fluorescent polarization immunoassay for whole blood everolimus determination using samples from renal transplant recipients

Objectives: This study compared the performance of a fluorescent polarization immunoassay (FPIA) against HPLC-tandem mass spectrometry (HPLC-MS) for the measurement of everolimus in renal transplant recipients. Design and methods: A total of 333 pre-dose samples from 45 renal transplant patients were analyzed by FPIA and HPLC-MS. Results: The inter-batch inaccuracy and precision of the FPIA for control samples were <= 6% and <= 13.0%, respectively (n = 17). The comparison of patient results yielded the Deming regression equation FPIA = 1.19 x HPLC-MS + 0.51. The mean bias was 24.4% (95% CI: -3.0 to 54.2%, range: -30.1% to 79.4%). Conclusions: The FPIA had acceptable analytical performance during the study but compared to HPLC-MS overestimated everolimus in patient samples. This overestimation is probably due to calibration differences between the methods and cross-reactivity of the FPIA antibody with everolimus metabolites. The clinical importance of the observed overestimation by FPIA requires further investigation. (c) 2006 The Canadian Society of Clinical Chemists. All rights reserved.