Can a patient with active inflammation involving circulating immune complexes have a normal complement level?
Yes. The serum level of complement components represents a balance between consumption and production. Complement components are acute-phase reactants, so their production by the liver increases with inflammatory states. If increased production keeps pace with consumption, the result will be a normal level of complement. Clinically, this means that while a decreased level of complement (C3, C4) is confirmatory evidence for complement consumption, normal complement levels cannot exclude complement consumption.