The complement system is composed of a set of circulating blood proteins that work together to promote protective immunity. Complement tests, most commonly C3 and C4, are used to determine whether deficiencies or abnormalities in the complement system are causing, or contributing to, a person's disease or condition. This test can be ordered for patients have unexplained infections, swelling, inflammation or symptoms of autoimmune disease Lupus. This test can be performed in Serum