Liquid chromatography with mass spectrometry (LC–MS/MS) is the method of choice for the determination of everolimus whole blood concentrations but is not always available. Therefore, immunoassays have been developed for clinical monitoring of everolimus. In previous studies, the Quantitative Microsphere System (QMS) immunoassay had a positive bias compared with LC–MS/MS, but was judged acceptable, although clinical agreement (eg, 95% limits of agreement) was not reported. The objective of this study was to assess whether the agreement between the QMS assay and an LC–MS/MS method was clinically acceptable for use interchangeably in therapeutic everolimus monitoring.
Whole blood samples from organ-transplanted patients on everolimus therapy were analyzed by both QMS (on Architect ci4100 analyzer) and LC–MS/MS. Paired results were compared using paired Student t test, Bland–Altman plots, and Deming regression analysis. The proportions of falsely supratherapeutic and subtherapeutic results on the QMS assay compared with the LC–MS/MS were calculated.
Among 250 samples (169 patients), mean everolimus concentrations determined by LC–MS/MS and QMS assays were 4.8 ± 2.1 ng/mL and 6.3 ± 2.1 ng/mL, respectively (P < 0.001), with 95% lines of agreement between −2.1 and 5.2 ng/mL, a range corresponding to 152% of the mean concentration. When stratified by the type of transplant, a similar positive bias was found in each subgroup (all P < 0.014). Sixty-nine percent of the samples yielding supratherapeutic concentrations (>8 ng/mL) on the QMS assay were within the therapeutic range on the LC–MS/MS.
The everolimus QMS immunoassay, using the Architect ci4100 analyzer, had a significant positive bias compared with LC–MS/MS, with a wide range between the limits of agreement. The lack of agreement may result in inadequate everolimus dose adjustments, suggesting that the QMS assay cannot be used interchangeably with the LC–MS/MS method for therapeutic everolimus monitoring in organ-transplanted patients.
*Laboratory of Toxicology, Pharmacology and Pharmacogenetics;
†Israel Poison Information Center; and
‡Clinical Pharmacology Unit, Rambam Health Care Campus, The Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa.
Correspondence: Yedidia Bentur, MD, Israel Poison Information Center, Rambam Health Care Campus, The Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, PO Box 9602, Haifa 31096, Israel (e-mail: email@example.com).
The study was partially supported by a grant from Novartis Pharma Services AG, Israeli Branch.
The authors declare no conflict of interest.
Received March 14, 2014
Accepted July 29, 2014