Evaluation of QMS everolimus assay using Indiko analyzer: comparison with an ultra-performance liquid chromatography-tandem mass spectrometry method.

Background: A new particle-enhanced turbidimetric immunoassay, Quantitative Microsphere System (QMS) everolimus, was evaluated using an Indiko analyzer (Thermo Fisher Scientific).

Methods: Analytical performances (imprecision, linearity, limit of detection, and limit of quantification) of this new immunoassay were evaluated. The method was compared with an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC/MS/MS) method and with the previously available Innofluor Certican immunoassay on 120 whole-blood samples from 74 transplant recipients. Passing-Bablok regression and Bland-Altman plot were used for method comparisons.

Results: Within- and between-day coefficients of variation were <10% at mean levels of 4.3, 8.2, and 15.9 ng/mL, respectively. This assay could be used at everolimus concentrations between 1.7 and 20 ng/mL. We obtained a Passing-Bablok regression of y = 0.99 × -0.15 (r = 0.95) when comparing with the UPLC/MS/MS method and of y = 0.81 × -0.09 (r = 0.94) when comparing with Innofluor assay. The mean and limits of agreement (mean ± 1.96 SD) of the difference between QMS everolimus and UPLC/MS/MS were -0.13 (from -2.0 to 1.74) ng/mL and were -1.19 (from -3.39 to 1.01) ng/mL between QMS everolimus and Innofluor.

Conclusions: The QMS everolimus method on Indiko analyzer demonstrated reliable and reproducible performances allowing routine monitoring in transplant patients.