Complement - 3

Function

The Complement C3 test measures the amount of C3 protein in the blood. C3 is a central component of the complement system, a complex group of proteins that form part of the innate immune system. Its primary role is to 'complement' or assist antibodies and phagocytic cells in clearing pathogens like bacteria and viruses from the body. It also triggers inflammation and helps remove damaged cells.

Why it is Ordered

Physicians order this test to monitor and diagnose autoimmune disorders. Because C3 is consumed during the inflammatory response, low levels often signal that an autoimmune process is highly active. It is particularly useful for tracking the progression of Systemic Lupus Erythematosus (SLE) and various forms of kidney inflammation (glomerulonephritis).

Associated Conditions

• Systemic Lupus Erythematosus (SLE): Low C3 levels are a hallmark of lupus 'flares,' indicating the immune system is attacking the body's own tissues.
• Glomerulonephritis: Inflammation of the kidney's filtering units can deplete C3 levels.
• Recurrent Infections: Inherited C3 deficiencies are rare but lead to a significantly increased risk of severe bacterial infections.
• Rheumatoid Arthritis: While C3 is often elevated in early inflammation, chronic consumption can occur in severe cases.