C4A and systemic lupus erythematosus: Among the SLE patients enrolled in this study, the prevalence of ANA, anti-dsDNA and anti-Sm were 96.50%, 65.00% and 43.75%, respectively; while the average serum C3 concentration was 0.51 ± 0.23 g/L, and the average C4 was 0.11 ± 0.06 g/L.