C3 and systemic lupus erythematosus: Among the SLE group, ANA, anti-dsDNA and anti-Sm antibody positive frequencies were 91.94%, 35.82% and 28.66%, respectively; while the average serum C3 concentration was 0.67 ± 0.30 g/L, and the average C4 was 0.15 ± 0.08 g/L.