Description

In the context of the complement system, "components 3 and 4" refer to C3 (complement component 3) and C4 (complement component 4), which are two key proteins that play a vital role in the immune response by helping to identify and destroy pathogens; they are often measured together in a blood test to diagnose conditions like autoimmune diseases due to their significant involvement in the immune system activation process. 

Fasting not required.