C3 and lupus nephritis: Laboratory test results: white blood count 2.92 × 109/L, C-reactive protein 7 mg/L, erythrocyte sedimentation rate 55 mm/H, protein in urine ++, 24-hour urine protein 740 mg, antinuclear antibody (ANA) 1:160, anti-Sm antibody positive, anti-SSA antibody positive, anti-U1RNP antibody positive, lupus anticoagulant positive, anti-β2 glycoprotein I-IgG positive, complement C3 0.392 g/L, complement C4 0.0286 g/L, renal biopsy: class V lupus nephritis.