Background: Therapeutic drug monitoring (TDM) of infliximab (IFX) and adalimumab is increasingly being used for the management of patients with inflammatory bowel disease (IBD) . Enzyme-linked immunoassays (ELISA) is one of the most used techniques; however, often requires batching samples which can delay results, and be inconvenient in urgent situations where a quick action is needed. In this study we compare the performance of a new lateral flow (LF) rapid test to detect anti-IFX antibodies with ELISA in IBD patients treated with either Remicade® (RMC) only or CT-P13 only or switchers from RMC to CT-P13.
Methods: Serum samples from IBD patients who participated in BIOSIM01, an observational retrospective study, in which patients were treated with either RMC only, or CT-P13 only, or CT-P13 following a switch from RMC, were used. In this study a total of 564 consecutive trough sera (corresponding to 103 patients) were collected just before the infusion to all patients. All samples were frozen for subsequent testing with ELISA (Promonitor® Anti-IFX, Progenika, Spain) and the LF rapid test (Promonitor® Quick Anti-IFX, Progenika, Spain). The rapid test is an immunochromatographic qualitative kit based on LF technology to detect anti-IFX antibodies in patients treated with any IFX molecule in human whole blood (fingerprick or venous) or serum. Antibody test results were read visually at 30 minutes. ELISA quantitative results were categorized as positive or negative to allow comparisons with the rapid test.
Results: The rapid test allowed the detection of anti-IFX antibodies in a few minutes with just 15 μL of serum and showed an almost perfect agreement with the comparative ELISA method. Overall, positive and negative percent agreements between ELISA and the LF test were 97.9% (CI95: 96.3–98.8), 96.0% (CI95: 88.9–98.6) and 98.2% (CI95: 96.5–99.0), respectively. No significant differences in the detection of Anti-IFX antibodies against either drug in any of the three cohorts were observed (Table 1). All antibody positive patients showed no detectable IFX levels as measured with ELISA.
Conclusions: The almost perfect agreement reported here between the LF and ELISA tests provides support to clinicians and laboratory personnel involved in biological drug monitoring in the use of the rapid test. The rapid test shows detection of antibodies aganist either the innovator or the biosimilar with comparable analytical sensitivity and offers a good solution in case a qualitative quick analysis of anti-IFX antibodies is required.
 Vande Casteele, (2015), Trough concentrations of infliximab guide dosing for patients with inflammatory bowel disease, Gastroenterology, 1320–9