P151 Anti-drug antibodies to Infliximab: a comparison of free anti-drug antibody measurement

Introduction Infliximab (IFX) is a biologic drug that inhibits the action of the pro-inflammatory cytokine, TNFα, which is implicated in the pathogenesis of inflammatory bowel disease (IBD). IFX has revolutionised the care of IBD patients, but response to the drug is not universal. Primary non-response to IFX treatment occurs in up to 30% of IBD patients while up to 46% of patients develop secondary loss of response.1 2 Development of anti-drug antibodies (ADAs) against IFX is considered a significant risk factor for the loss of response to treatment, hence the measurement of ADAs as part of therapeutic drug monitoring is an increasingly utilised tool. The detection of ADAs varies widely depending on the type of assays used. The aim of this study was to determine the qualitative concordance of three commercially available ELISA kits for measurement of free ADAs to IFX on the Grifols Triturus analyser. Methods 150 patient samples with low IFX drug levels (≤0.6µg/ml) were analysed for free ADAs using Promonitor, Lisa Tracker and IDKmonitor kits on the Grifols Triturus automated ELISA analyser. Results Kappa coefficient (κ) analysis indicated a moderate agreement between the Promonitor and IDKmonitor assays (κ =0.484 (95% CI, 0.357 to 0.611)) and the IDKmonitor and Lisa Tracker assays (κ = 0.485 (95% CI, 0.348–0.621)) as well as substantial agreement between the Promonitor and Lisa Tracker assays (κ =0.768 (95% CI, 0.667–0.870)). Figure 1 shows the distribution of samples identified as free ADA positive by each kit. Conclusion Although broad qualitative agreement was found between the three kits, they should not be used interchangeably for patient management. All kits appear amenable for utilisation in a high-throughput laboratory though a true quantitative comparison between these kits was precluded by the absence of any certified reference material for free ADAs to IFX. Further research is required to estimate the impact of free ADAs on efficiency of IFX treatment and patient management. References Ben-Horin S and Chowers. Aliment Pharmacol Ther 2011; 33: 987–995 Osterman MT, Haynes K, Delzell E, et al. Clin Gastroenterol Hepatol 2014;12:811–817