### What is Complement C4 Testing? Complement C4 testing measures the level of C4 proteins in your blood. These proteins are part of the complement system, which helps your immune system fight infections and remove dead cells. ### Why is C4 Testing Important? Doctors use C4 tests to monitor chronic diseases and autoimmune disorders. Changes in C4 levels can indicate how well your body is responding to treatment or if there is an ongoing inflammation. ### Who Needs a C4 Test? You might need a C4 test if you have symptoms of chronic infections, kidney problems, hepatitis, or autoimmune diseases like rheumatoid arthritis and lupus. For instance, people with lupus often have low C4 levels during flare-ups. ### How is the Test Done? The test is a simple blood draw, usually from a vein in your elbow or hand. No special preparation is needed, but inform your doctor about any medications you are taking. ### Understanding the Results - **Normal Range:** 15-45 mg/dL - **Low Levels:** May indicate autoimmune diseases, chronic infections, or improper sample handling. - **High Levels:** Could be due to recent injury, infection, cancer, or inflammatory bowel disease. ### Conclusion C4 testing is a valuable tool for doctors to monitor and manage chronic diseases and autoimmune disorders. Always discuss your results with your doctor to understand what they mean for your specific health condition.