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Background Adalimumab (ADL), infliximab (IFX) and their biosimilars are widely used biological drugs. Some patients, however, generate neutralizing antibodies that hamper the effectiveness of these drugs. Evidence shows therapeutic drug monitoring of serum levels ADL/IFX and anti-drug antibodies (ADA) is useful to improve treatment effectiveness. We evaluated a new rapid quantitative method, Quantum Blue (QB), for determining serum anti-ADL and anti-IFX antibodies (Research Use Only labelling) by comparing it with two established ELISA kits, Promonitor (PM) and Lisa-Tracker (LT). Methods Eighty samples (40 for each drug type) were analysed. Percentage of agreement and kappa statistic were used to compare positive/negative ADA results. Clinical implications for drug treatment in the patients with discordant results were evaluated. The Chi-square test was used to analyze differences for ADA detection in patients with disease flare and without concomitant immunosuppressant treatment. Results Agreement exceeded 80 % among anti-ADL methods. Although LT ELISA showed a lower capacity in detecting anti-ADL antibodies, discrepancies were found for levels close to the cut-off concentration, thus having minimal impact on clinical decisions. Conversely, QB anti-IFX displayed low agreement with PM and LT ELISA kits (67.5 % and 50 %, respectively), and was unable to detect high levels of antibodies, therefore having major clinical implications. Agreement between PM and LT ELISA anti-IFX kits was 82.5 % with all discordant results being undetected for PM and slightly positive for LT. Conclusion QB anti-ADL shows similar performance to ELISA kits while QB anti-IFX needs further improvements to achieve reliable antibody detection.

Background Anti-drug-antibodies (ADA) against infliximab are frequently measured in patients receiving infliximab treatment with loss of response and undetectable infliximab concentrations. Different ADA bridging assays (1st generation, 2nd generation and ready-to-use kit) have been developed successively and were applied over the last 10 years, making comparison between ADA concentrations very challenging. A cutoff of 8 μg/ml was established to discriminate low from high ADA concentrations using the 1st generation ADA bridging assay. The objective of this study was to enable comparison of ADA concentrations determined with the different assays that were developed over the years. Methods 166 serum samples were collected from patients with inflammatory bowel disease treated with infliximab. 98 samples were measured simultaneously with the 1st and 2nd generation ADA assay, 67 serum samples were measured with the 2nd generation assay and the ready-to-use kit. Results From our ADA concentration comparison experiments, we deduced that the previously established cutoff of 8 μg/ml with the 1st generation ELISA has a similar impact as the cutoff of 374 ng/ml with the 2nd generation ELISA and a cutoff of 119 ng/ml in the ready-to-use ELISA kit. Conclusion ADA concentrations measured with the different assays were compared and a cutoff concentration was determined for each of them to distinguish between low and high ADA concentrations. These cutoff concentrations may serve as a tool for clinicians to make treatment decisions for patients with a loss of response to infliximab and undetectable infliximab serum concentrations.