The method of complement C3 and C4 examination is mainly through blood sampling and laboratory tests. Normally, human blood C3 levels are 800-1550 mg/L and C4 levels are 130-370 mg/L. Blood complement levels and activity are altered in many pathological situations, so changes in complement levels should be observed dynamically in clinical practice. Decreased complement levels do not necessarily represent immune dysfunction and immunodeficiency because in ischemic coagulation necrosis and toxic necrosis, tissues can release more proteolytic enzymes, resulting in a decrease in complement hemolysis activity and complement grouping. Generally elevated blood complement concentrations are seen in various inflammatory diseases, obstructive jaundice, acute myocardial infarction, ulcerative colitis, diabetes mellitus, gout, acute rheumatic fever, polymyositis, and mixed connective tissue disease.