Objective: To establish thresholds for rheumatoid arthritis (RA) activity categories according to the RA Disease Activity Index-5 (RADAI-5).
Methods: Three hundred ninety-two patients with RA were categorized according to Disease Activity Score 28-joint count (DAS28), Clinical Disease Activity Index (CDAI), and their satisfaction (PATSAT) with disease status. These measures built the basis for the calculation of disease activity limits for the RADAI-5. Patient assessments simultaneously meeting the identical DAS28, CDAI, and PATSAT categories were taken as the references to establish the thresholds for the respective RADAI-5 categories by calculating the third quartile of the corresponding RADAI-5 values. Subsequently, these new thresholds were applied to all assessments.
Results: Seven hundred fifty-eight assessments in 392 patients (2 assessments median/patient) could be obtained, most patients having mild to moderate disease according to DAS28 and CDAI. Calculating the third quartile, the RADAI-5 thresholds were as follows: 0.0-1.4 for a remission-like state, 1.6-3.0 for mild disease activity, 3.2-5.4 for moderate, and 5.6-10.0 for high disease activity. Categorization according to the RADAI-5 showed a normal distribution, while DAS28 and CDAI were somewhat shifted to the left. DAS28 and CDAI levels, as well as tender and swollen joint counts and physician's global assessment and erythrocyte sedimentation rate, proved to be highly significantly different within the different RADAI-5 categories (Kruskal-Wallis test p < 0.001).
Conclusion: RADAI-5 thresholds for RA activity could be elaborated. Patient self-report questionnaires may substitute composite disease activity scores and may contribute significantly to improving documentation in routine patient care.