C3 and acute kidney injury: In comparison with the non-AKI group, patients with AKI had significantly higher proportions of serositis (P < 0.001), neurologic disorder (P = 0.026), anemia (P < 0.001), thrombocytopenia (P = 0.013), and nephrotic syndrome (P = 0.011), but significant lower serum C3 (P < 0.001).