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 ...

C4 has talked plenty about what he’s mad about, about bad news over the last 11 months. But for Thanksgiving, what does the talk host have to be thankful for? He said he’s optimistic about how the ...