CRP and rheumatoid arthritis: The result show that blood circulating copper was positively correlated with CRP (r = 0.45, P < 0.01) and ESR (r = 0.58, P < 0.01), while blood circulating iron was negatively correlated with CRP (r =  − 0.46, P < 0.01) and ESR (r =  − 0.56, P < 0.01) in RA.