Complement C3 details

Complement C3 is one of the central proteins in your complement system, a group of proteins that work together as part of your immune system's defense against infection and help clear immune complexes from your blood. Low C3 can indicate that the complement system is being actively consumed — a pattern often seen during active flares of autoimmune conditions like lupus, or during certain infections and kidney conditions (glomerulonephritis). It's typically tested alongside C4 and sometimes total complement (CH50), since the specific pattern of C3 and C4 levels together can help point toward the underlying cause and, in known autoimmune conditions, help track disease activity over time.