C4A and irritable bowel syndrome: In the IBS-M subgroup, the serum levels of C3 (median [147.2 mg/dL]; range [85.10 mg/dL–213.2 mg/dL]) and C4 (median [28.40 mg/dL]; range [11.20 mg/dL–51.60 mg/dL]) were significantly higher compared to the HC group (C3 median [131 mg/dL]; range [75.60 mg/dL–205 mg/dL]; p = 0.0224; C4 median [23.80 mg/dL]; range [13.70 mg/dL–34.20 mg/dL]; p = 0.0259).