C4A and systemic lupus erythematosus: Furthermore, C3 [0.54 (0.34–0.77) g/L], C4 [0.09 (0.04–0.12) g/L] and albumin [37.65 (30.88–42.80) g/L] serum levels were lower in the SLE group compared with the OADs group and healthy controls (p < 0.05).