Also known as: C4, Body Fluid, Complement C4 (β1E), Body Fluid.

Complement testing may be ordered to diagnose the cause of angioedema, recurrent microbial infections, or inflammation. It may be used to help diagnose and monitor the activity of acute or chronic autoimmune diseases such as systemic lupus erythematosus (SLE). It may be tested and monitored with immune complex-related diseases and conditions such as: rheumatoid arthritis, glomerulonephritis, serum sickness, and vasculitis. When immune complexes form, complement will help to clear them from the blood, making levels of complement low.