The reference value of serum total complement activity 50 (CH50) is generally 50-100 U/L. Due to the different testing methods, its specific reference value also has some differences, and it is recommended to take the actual situation as the basis. Complement has the functions of lysing target cells, promoting phagocytosis, participating in inflammatory reactions, etc. Meanwhile, complement also plays a key role in immune regulation, clearing immune complexes, stabilizing the internal environment of the body, and participating in metabolic reactions and autoimmune diseases. The determination of total complement mainly reflects the activity program of complement activation through traditional pathways. The normal reference range of serum total complement activity 50 (CH50) is generally 50-100 U/L. When the body suffers from infections, autoimmune diseases and tumors, the serum total complement activity 50 (CH50) index will be abnormal. Increased serum total complement activity 50 (CH50) is most often seen in acute inflammatory infections, acute stages of rheumatic fever, myocardial infarction, tumors, etc. Decreased serum total complement activity 50 (CH50) is usually seen in acute glomerulonephritis, active stage of systemic lupus erythematosus, and chronic liver disease. Serum total complement activity 50 (CH50) is often used as an adjunctive test to diagnose the disease, and usually needs to be combined with the patient’s symptoms, humoral immune function, autoantibodies, imaging and other related tests to diagnose the disease. If abnormalities of CH50 are found, it is recommended to seek medical advice in a timely manner and follow the doctor’s instructions for standardized diagnosis and treatment.