Lack of Interchangeability Between 3 Different Methods for Quantification of Everolimus in Blood: ACMIA, LTIA, and UHPLC-MS/MS.

Background: Affinity chrome-mediated immunoassays (ACMIA) do not require pretreatment and have a wide calibration range and good analytical performance. To date, no studies have compared ACMIA and latex agglutination turbidimetry immunoassays (LTIA). The objective of this study was to evaluate the interchangeability of ACMIA, LTIA, and the previously developed ultra-high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS).

Methods: A total of 111 whole blood samples were collected from 25 patients undergoing routine everolimus therapeutic drug monitoring. The interchangeability between the 3 methods was assessed using robust Passing-Bablok regression analysis and Bland-Altman plots.

Results: All samples were quantifiable by UHPLC-MS/MS, whereas 56 and 1 samples were below the lower limits of quantification by LTIA and ACMIA, respectively. In the robust Passing-Bablok regression plots, the slopes of the regression equations between ACMIA and UHPLC-MS/MS, LTIA and UHPLC-MS/MS, and ACMIA and LTIA were 1.23 (95% [confidence interval] CI, 1.13-1.33), 0.67 (95% CI, 0.57-0.77), and 1.71 (95% CI, 1.43-2.33), respectively, with significant proportional biases indicating no interchangeability among all 3 methods. Bland-Altman plots also revealed statistically significant proportional biases between ACMIA and UHPLC-MS/MS (P = 0.012), LTIA and UHPLC-MS/MS (P < 0.001), and ACMIA and LTIA (P < 0.001).

Conclusions: Statistically significant proportional biases were observed among the 3 methods. Blood everolimus concentration measurements should be interpreted with caution when switching the quantification methods for therapeutic drug monitoring.