Basic components of the immune system part 103

Complement Assays

Perhaps the most useful assays for complement are the immunochemical assays of C3 and C4. As noted, which outlines the alternative and classical modes of complement breakdown, a low C3 and C4 but normal factor B suggest that activation of the classical pathways has occured. Examples would be patients with systemic lupus erythemathosus or vasculitis. In contrast, if C3, C4, and factor B are all low, the alternative pathway is also activated via either feedback loops or simultaneous activation. This would point to a gram negative bacteremia. Normal C4 levels with low C3 and factor B levels suggests acute or  chronic infection. Acute rheumatic fever is such an example.