My baby has a low C4 count - explain please!?

What's the age? If you have a premature infant, chances are that the level represents chronic lung disease/hx or respiratory distress. Autoimmune diseases also can be associated with C4 decreases, however, other studies are indicated. C3 and C4 are the most commonly measured complement components. Complement activity may be measured to determine how severe a disease is or if treatment is working.