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Labcorp
Broadest draw-site network nationwide.
Quest Diagnostics
Same-day appointments in most metros.
Complement C3 is a protein in the immune system that plays a key role in the complement cascade, which helps fight infections and clear damaged cells. A C3 test measures its levels in the blood and is often used to evaluate immune function or inflammatory conditions. Low C3 levels may indicate autoimmune diseases like systemic lupus erythematosus (SLE) or complement system deficiencies, while elevated levels can be seen in acute or chronic inflammation.
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