C3 and systemic sclerosis: There were no differences in C3 and C4 levels between SSc patients and HC (1.07 g/L (IQR 0.99–1.12 g/L) vs. 0.84 g/L (IQR 0.66–0.98 g/L) and 0.2 g/L (IQR 0.16–0.23 g/L) vs. 0.36 g/L (IQR 0.27–0.41 g/L), respectively; p > 0.05).