This assay employs the competitive inhibition enzyme immunoassay technique. An antibody specific for Complement Component 3 (C3) has been pre-coated onto a microplate. A competitive inhibition reaction is launched between Horseradish Peroxidase (HRP) labeled Complement Component 3 (C3) and unlabeled Complement Component 3 (C3) (Standards or samples) with the pre-coated antibody specific for Complement Component 3 (C3). After incubation the unbound conjugate is washed off. The amount of bound HRP conjugate is reverse proportional to the concentration of Complement Component 3 (C3) in the sample. After addition of the substrate solution, the intensity of color developed is reverse proportional to the concentration of Complement Component 3 (C3) in the sample.