ESR1 and rheumatoid arthritis: Regarding variables related to RA disease activity, the rate of RF+ (p < 0.0001) and levels of RF (p < 0.0001), ESR (p < 0.0001), CRP (p = 0.0012), and DAS28-ESR (p = 0.0001) were significantly different among the groups and correlated with anti-CCP levels.