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.

Complement 3 glomerulopathy (C3G) is a rare kidney disease that affects your body’s innate immune system (complement system). Complement 3 glomerulopathy (C3G) is a kidney disease that’s caused by ...

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 ...