Fig. 2

Boxplots of the serum anti-citrullinated protein antibody (ACPA) levels in four groups of subjects. The medians of ACPA levels between the groups were compared with Kruskal–Wallis test (between group, p = 0.005), which indicates significant difference between groups at p < 0.05. Pairwise Mann–Whitney U-test **statistically significant difference inter-group at p < 0.05