Complement C3(C3) Determination Reagent(Immunoturbidimetry) is an in vitro diagnostic quantitative test kit. This test is used for Assessing disease activity in systemic lupus erythematosus or investigating an undetectable total complement (CH50) level. C3 is part of the complementary immune system. The complementary immune system is part of the larger innate immune system that serves as the body's frontline defense against disease, attacking anything that the body considers abnormal.