THU0266 Determining the Absolute Change in the Clinical Disease Activity Index (CDAI) to Define A Minimally Important Difference

Background Simplified measures to quantify rheumatoid arthritis (RA) disease activity are increasing in clinical practice. The absolute minimally important difference (MID) in these measures, such as the clinical disease activity index (CDAI), has not been well defined in real-world settings, especially for early RA patients (ERA) with low or moderate disease activity. Objectives To determine the MID for improvement of the CDAI in a “real world” setting using an cohort of patients with ERA. Methods Data from the Canadian CATCH cohort of patients with ERA were used to identify pairs of rheumatology visits 3 months apart occurring within 12 months of cohort entry. Patients with concomitant fibromyalgia (8%) were excluded. Absolute change in CDAI was examined between visit pairs and correlated with relevant changes corresponding to MIDs in patient self-reported improvement (better vs. same/worse), patient pain (>1 vs. ≤1, and >2 vs. ≤2) and HAQ (>0.22 vs. ≤22, and >0.30 vs. ≤0.30). The 10th and 90th percentile of the CDAI distributions for EULAR good response vs. non-response in DAS28 ESR (>1.2 vs.