C3 and Behcet disease: Serum C3 levels in BD patients (0.998 ± 0.185 g/L) were significantly lower (t = 2.76, df = 290, P = 0.003) than that in HC group (1.064 ± 0.219 g/L), while the serum UA levels were significantly elevated (t = −2.068, df = 290, P = 0.0195) in BD patients (354.64 ± 90.37 vs. 332.96 ± 88.70 μmol/L).