This human complement component 3 antigen assay is intended for the quantitative determination of total complement component 3 antigen in human plasma, serum, urine, milk, saliva and cell culture samples. Human C3 will bind to the capture antibody coated on the microtiter plate. After appropriate washing steps, biotin labeled anti human C3 primary antibody binds to the captured protein. Excess primary antibody is washed away and bound antibody is reacted with peroxidase conjugated streptavidin. Following an additional washing step, TMB substrate is used for color development at 450nm. A standard calibration curve is prepared along with the samples to be measured using dilutions of human C3. Color development is proportional to the concentration of total C3 in the samples.