OBJECTIVE: To determine whether the Simplified Disease Activity Index (SDAI) and 
the Clinical Disease Activity Index (CDAI) are equally applicable for the total 
population with rheumatoid arthritis (RA).
METHODS: Five hundred and fifty-seven outpatients with RA [432 females, 125 
males; median age 64 years (range 18-85); median disease duration 48 months 
(range 2-548)] were enrolled consecutively in this cross-sectional study. SDAI, 
CDAI, patient's assessment of pain on the visual analogue scale (VAS) 0-100, 
rheumatoid factor (RF), and disease duration were recorded. Linear regression 
analysis was performed for each confounding factor.
RESULTS: The median SDAI for all 557 patients was 11.6 (range 0.07-46.60) and 
the median CDAI was 10.7 (0.00-42.10). The median SDAI was 12.2 (0.07-46.60) in 
females and 8.0 (0.10-35.20) in males. The respective medians for the CDAI were 
11.3 (0.00-42.10) and 7.1 (0.00-32.00). These differences were highly 
statistically significant (p<0.001). Patient's assessment of pain on the VAS 
0-100 scale had a median value of 32 mm. Regression analysis revealed a highly 
significant relationship between SDAI/CDAI levels and patient's pain rating 
(SDAI: r = 0.660, p<0.001; CDAI: r = 0.671, p<0.001). On multiple regression 
analysis, pain exerted a highly significant influence on SDAI and CDAI levels 
(p<0.001), whereas age, disease duration, and RF were not correlated with either 
level.
CONCLUSION: SDAI and CDAI values are highly dependent on the patient's pain 
perception and gender. The effects of patient's age, disease duration, and RF 
were inconclusive with respect to the values of the respective disease activity 
indexes.