A C4 and C3 complement blood test is a type of test that measures the levels of C4 and C3, which are proteins that are part of the complement system in the blood. The complement system is a group of proteins that work together to help the immune system fight infection and inflammation. This test is commonly ordered to help diagnose and monitor autoimmune disorders, such as lupus and rheumatoid arthritis, and to evaluate the effectiveness of treatment for these conditions.
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