Monitoring of Infliximab Trough Levels and Anti-Infliximab Antibodies in Inflammatory Bowel Diseases: A Comparison of Three Commercially Available ELISA Kits.

Background: There are many studies presenting data of biologics and several ELISA kits commercially available for monitoring infliximab serum trough levels (s-IFXt) and anti-drug antibodies (ADAb). We propose to compare technical characteristics and results of three different assays on a cohort of 35 patients under infliximab (IFX) and suffering from inflammatory bowel disease (IBD). Patients and methods: s-IFXt and ADAb were systematically measured with three ELISA kits: Lisa-Tracker (R) Duo infliximab (Theradiag (R)), Ridascreen (R) IFX Monitoring (R-Biopharm AG (R)) and Promonitor (R) IFX (Progenika Biopharma SA (R)). Results: The main technical features that differed between kits for measuring s-IFXt were: (i) TNF coating, (ii) immune complexes revelation strategy and/or (iii) interference with other anti-TNF alpha agents. For kits measuring ADAb, they were revelation steps and unit of results. There was an excellent mathematical correlation of s-IFXt between assays however Bland-Altman analysis denoted (i) s-IFXt were on average 48 to 69% higher in Ridascreen (R) than in the other two assays, and (ii) elevated s-IFXt were higher with Promonitor (R) compared to Lisa-Tracker (R). As a consequence, there were some substantial discrepancies between assays for classification of s-IFXt into concentration ranges. Despite unstandardized units, pairwise qualitative comparison showed a perfect agreement between the three pairs of ADAb assays. Conclusion: Our data show that the evaluated assays are not quantitatively interchangeable due to substantial variations in some results that could lead, for some patients, to divergent therapeutic decisions. We remind to be cautious when comparing study results issued from different kits and recommend using the same assay for the longitudinal follow-up of IBD patients.