Complement, Total details

This test, often called CH50, measures the overall functional activity of your complement system as a whole, essentially checking whether all the individual complement proteins are present in adequate amounts and working together properly to carry out a normal immune reaction. A low or absent CH50 can point toward either an inherited deficiency in one specific complement component (in which case CH50 is often very low or undetectable) or an acquired reduction from a condition like active lupus that's consuming complement faster than it's being replaced. It's typically used alongside individual C3 and C4 levels to help pinpoint exactly which part of the complement system is affected.