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 ...

However, the discovery that receptors for complement activation fragments are expressed by almost all immune cells — including B cells and T cells — and that these cells can sense and convert the ...

These findings suggest complement protein levels may be an important biomarker for type 1 diabetes. Disruption of the complement system appears to precede the onset of islet autoimmunity (IA), making ...

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 ...