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OBJECTIVE: To determine if the Disease Activity Index including a 28-joint count (DAS28) is equally applicable for the total population with rheumatoid arthritis (RA). METHODS: Five hundred fifty-seven outpatients with RA [432 women, 125 men; median age 64 yrs (range 0-85), median disease duration 48 mo (range 2-548)] were enrolled consecutively into this cross-sectional study. DAS28, physician's global assessment of disease activity, patient's assessment of pain on visual analog scale, C-reactive protein (mg/dl), rheumatoid factor (RF), and disease duration were recorded. t-tests were applied for all comparisons of DAS28 values. Linear regression analysis was performed for each confounding factor. RESULTS: The mean DAS28 in female patients was 3.66 +/- 0.57 SEM, and in males 3.01 +/- 1.12 (p < 0.001). DAS values in patients with early RA (< 37 mo) were significantly higher than in patients with advanced RA (3.62 +/- 0.67 vs 3.37 +/- 0.81, respectively; p < 0.017). Regression analysis revealed a highly significant relationship between DAS28 score and patient's pain rating (r = 0.592, p < 0.0001). Pain exerted the greatest influence on the DAS28 (p < 0.0001), while of the other factors only age (p < 0.008 for females, p < 0.007 for males) was also significantly correlated with the DAS28 values. CONCLUSION: DAS28 values differ considerably depending primarily on the patient's pain perception and gender and to a lesser degree on patient's age, whereas results for disease duration and RF were inconclusive.