Complement component 3, often called C3, is an essential protein of the immune system. This protein plays a vital role in the body’s innate immune system, providing the first line of defense against ...

A complement blood test measures how well complement proteins in your blood support immune defense. The complement system helps antibodies fight germs and clear foreign substances. Complement testing ...

Your complement system consists of a group of important proteins in your bloodstream. These proteins help your immune system fight off harmful invaders, such as bacteria, and other foreign substances.

A complement C4 (also known as a complement component 4, or simply C4) is a test to measure the level of C4 proteins you have in your blood. These proteins play a role in how your immune system ...