Among the three groups, the angiotensin‐converting enzyme (ACE) index was higher in RA than in N (254.49 ± 18.44 vs. 104.37 ± 13.97, P < 0.001) and it was higher in DM than in N (249.71 ± 28.03 vs. 104.37 ± 13.97, P < 0.001). Here, ACE is linked to rheumatoid arthritis.