CRP and rheumatoid arthritis: The linear association between the level of trace elements and other parameters and the RA disease activity showed that hemoglobin levels (r =  − 0.41, P < 0.01) and blood iron (r =  − 0.37, P < 0.01) were negatively correlated with DAS28-CRP (Supplementary Table 2, Fig. 4A, B).