Objectives To determine disease activity levels and clinically important changes with the recently developed and validated [1] EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI), and to assess their relevance for conducting clinical trials. Methods Patients from 2 large prospective cohorts (EULAR [multicenter international] n=395, ASSESS [multicenter French] n=395), have been followed for 6 months and 1 year, respectively. Physician completed ESSDAI, evaluated disease activity according to a 4 point scale, and assessed if the patients were in minimal disease activity (MDA). A ROC curve analysis and an anchoring method using MDA definition was used to determine disease activity levels of ESSDAI. At follow-up visit, physicians assessed whether disease activity has improved or not. An anchoring method based on this evaluation of change was used to estimate the minimum clinically important improvement (MCII) of ESSDAI. Data from recent clinical trials evaluating biologics [2-4] were used to assess the relevance of these thresholds. Results According to data from the 2 cohorts, low (ESSDAI <5), moderate (5 ≤ ESSDAI ≤13) and high (ESSDAI≥14) activity levels were defined. Fifty-four and 37% of patients from EULAR and ASSESS real life cohorts and 70 to 77% of patients from recent trials had at least moderately active disease (ESSDAI≥5). The MCII of the ESSDAI was defined as an improvement of at least 3 to 4 points. Based on recent trial data, the cutoff of 3 could be retained, because it was the best to discriminate between patients from placebo and treated arms. Conclusions In conclusion, this study, involving 2 independent large cohorts of primary SS patients allows determining disease activity levels and clinically relevant changes with ESSDAI. We hope that the results of this study will help to conduct more effectively clinical trials for evaluation of biologics in primary SS. Our proposal is to use the threshold of moderate activity as entry criteria (patients with ESSDAI≥5), and to define response to treatment as a significant improvement of ESSDAI (at least 3 points). References Seror R, Theander E, Brun JG, et al. Validation of EULAR primary Sjogren's syndrome disease activity (ESSDAI) and patient indexes (ESSPRI). Ann Rheum Dis 2014. Mariette X, Seror R, Quartuccio L, et al. Efficacy and safety of belimumab in primary Sjogren's syndrome: results of the BELISS open-label phase II study. Ann Rheum Dis 2013. Meijer JM, Meiners PM, Vissink A, et al. Effectiveness of rituximab treatment in primary Sjogren's syndrome: a randomized, double-blind, placebo-controlled trial. Arthritis Rheum 2010;62:960-8. Devauchelle-Pensec V, Mariette X, Jousse-Joulin S, et al. Tolerance and efficacy of Rituximab in primary Sjögren's syndrome (TEARS): Results of a randomized controlled trial. Ann Rheum Dis 2012;71:75. Disclosure of Interest None declared DOI 10.1136/annrheumdis-2014-eular.4399