There are multiple complement proteins in the body. Some exist in the serum, and some bind to
IgG. The major complement proteins that bind to IgG are C3b and C3d. After IgG binds to an
antigen, such as dairy or gluten, if it encounters C3 in the serum, it will create the cleavage of C3
into C3b, which binds to multiple sites on IgG. It will be degraded, and finally form C3d, which also
binds to IgG. By measuring multiple types of complement that bind to IgG, you are more likely to
identify the IgG titers that have the most inflammatory potential in the patient. Measuring
multiple steps in the complement cascade creates paints a more clear picture of overall
complement activation.
