Performance of Routine Assessment of Patient Index Data 3 (RAPID3) for assessment of rheumatoid arthritis in clinical practice: differential agreement of RAPID3 according to disease activity categories.

To evaluate the performance of Routine Assessment of Patient Index Data 3 (RAPID3) with the disease activity score 28 (DAS28) and the clinical/simplified disease activity index (CDAI/SDAI) in a Korean population with rheumatoid arthritis (RA). Four hundred patients with RA were consecutively enrolled. All patients completed disease activity indices such as RAPID3, DAS28, SDAI, and CDAI. The kappa and/or weighted coefficients were used to assess agreement between RAPID3 and other disease activity indices. ANOVA, Mantel-Haenszel chi-square test, and Spearman's partial correlation analysis were used for analyses. RAPID3 scores were significantly correlated with DAS28 (r = 0.62), SDAI (r = 0.74), and CDAI (r = 0.75; p < 0.0001 for all indices) and other activity measures including swollen/tender joint counts, erythrocyte sediment rate, and C-reactive protein. The weighted kappa coefficients of RAPID3 with DAS28, SDAI, and CDAI among the four disease activity categories were 0.33, 0.34, and 0.33, respectively. Kappa coefficients for RAPID3 in two disease activity categories increased more than four categories (κ = 0.40-0.42) indicating fair agreement. More than 86 % of patients with high-to-moderate disease activity in DAS28, CDAI, and SDAI had high-to-moderate disease activity using RAPID3 criteria. However, approximately 50 % of patients with remission-to-low disease activity in DAS28, CDAI, and SDAI showed remission-to-low disease activity in RAPID3. This study confirms RAPID3 as an informative disease activity index with equivalent values in DAS28, CDAI, and SDAI. RAPID3 reveals differential agreement in patients with lower disease activity.