BACKGROUND: An index is needed to assess the status of patients with rheumatoid arthritis (RA), as none of the existing measures are applicable to all individual patients. The 28-joint Disease Activity Score (DAS28) is the most specific and widely used index. Routine Assessment of Patient Index Data (RAPID3) is an index containing only the 3 patient self-report core dataset measures, without a laboratory test or formal joint count, and with simple scoring. RAPID3 is correlated significantly with DAS28, but calculated in 5-10 seconds on a Multidimensional Health Assessment Questionnaire (MDHAQ), compared to 114 seconds for DAS28. METHODS: DAS28 (0-10 scale) categories for high, moderate, and low activity, and remission (≤ 2.6, 2.6-3.2, 3.21-5.1, and > 5.1, respectively) and proposed RAPID3 (0-30 scale) categories for severity (0 ≤ 3, 3.1-6, 6.1-12, and > 12) were compared in patients taking abatacept and control-treated patients at the endpoint of the Abatacept in Inadequate Response to Methotrexate (AIM) and the Abatacept Trial in Treatment of Anti-TNF INadequate Responders (ATTAIN) clinical trials, using cross-tabulations and kappa statistics. RESULTS: Overall, 92%-99% of patients classified as having high DAS28 activity had high or moderate RAPID3 severity, while 64%-83% in DAS28 remission had RAPID3 low severity or remission; 50%-82% of patients with good or poor EULAR responses had good or poor RAPID3 responses. Kappa values ranged from 0.25 to 0.48, and weighted kappas from 0.32 to 0.52, indicating fair to moderate agreement for the 2 indices. CONCLUSION: Proposed RAPID3 severity and response categories yield comparable results to DAS28 and EULAR criteria in AIM and ATTAIN. DAS28 is more specific for clinical trials. RAPID3 does not preclude also scoring DAS28, and may be informative in the infrastructure of routine care.