Serum or plasma mass concentration of complement component C3

What Does C3 Do in Your Body?

C3 is part of the complement system, a network of proteins that enhance your immune response. It helps identify and destroy harmful bacteria, viruses, and other invaders. It also plays a role in regulating inflammation and immune reactions, including those triggered by autoimmune conditions.

Why Might You Need This Test?

Doctors may order C3 testing if you have symptoms of immune disorders (e.g., infections, autoimmune diseases like lupus or rheumatoid arthritis), kidney problems, or if your immune system isn’t working as expected. It can also help monitor treatment progress for conditions affecting the complement system.

What Could Low or High C3 Levels Mean?

Low C3 levels may indicate immune dysfunction, chronic infections, or certain autoimmune diseases. High levels could suggest acute inflammation or overactive immune responses, though this is less common. Always discuss results with your healthcare provider.

How Is This Test Done?

A blood sample is drawn from a vein, usually in your arm. The blood is processed to separate serum or plasma, where C3 is measured using a lab technique (like nephelometry or immunoassay). Results are reported as a mass concentration.