CRP and immunoglobulin G4-related sclerosing disease: Among patients with only a single affected organ, patients with IgG4-RD had significantly lower serum C-reactive protein (CRP) levels (median 0.10 mg/dL vs 0.31 mg/dL; p = 0.020), higher serum IgG4/IgG ratios (22% vs 12%; p = 0.027), and lower total haemolytic complement activity (CH50) (38.0 U/mL vs 48.9 U/mL; p = 0.044) than patients without IgG4-RD.