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 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 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 ...

For the first time in a long time, the Bears had a full complement of healthy wide receivers at practice. On Monday, Velus Jones Jr. and Byron Pringle each returned from their injuries. Waiver claim ...

A complement blood test checks for autoimmune diseases or other issues with your immune system. Your doctor might test you if you have a family history of certain conditions, such as rheumatoid ...