There are several reasons why you might have high complement C4 levels over 45 milligrams per deciliter. If you have had a recent injury or infection, you’re likely to have more C4 in your blood.

The complement system, which was discovered more than 100 years ago, is one of the oldest components of immunity and is central to the detection and destruction of invading pathogens 1,2,3,4,5.

Researchers have discovered that SARS-CoV-2 hijacks three important host proteins that dampen the activity of the complement system, a key component of early antiviral immunity. This significantly ...