Background: This study compared the performance of plasma infliximab and adalimumab quantification using a commercially available kit (mAbXmise kit) and mass spectrometry readout to that of two ELISA methods in patients treated for inflammatory bowel disease. Methods & results: The mAbXmise method based on liquid chromatography tandem mass spectrometry (LC-MS/MS) was linear from 2 to 100 μg/ml. It was validated according to international guidelines. Regarding cross-validation for infliximab (n = 70), the mean bias with LC-MS/MS assay was approximately threefold higher with the commercial ELISA assay compared with the in-house ELISA (-6.1 vs -1.8 μg/ml, respectively). The mean bias between the LC-MS/MS assay and in-house ELISA was -1.2 μg/ml for adalimumab (n = 35). Conclusion: The LC-MS/MS method is a powerful alternative to immunoassays to monitor concentrations of infliximab and adalimumab.
Keywords: ELISA; LC-MS/MS; adalimumab; infliximab; therapeutic drug monitoring.