The Calbiotech hCG ELISA is an adapted solid phase sandwich ELISA method. The samples, biotin labeled anti-hCG and anti-hCG-HRP conjugate are added to the wells coated with Streptavidin. hCG in the patient's serum binds to binds to the anti-hCG antibodies and forms a sandwich on the streptavidin coated plate. Unbound protein and HRP conjugate are washed off by wash buffer. Upon the addition of the substrate, the intensity of color is proportional to the concentration of hCG in the samples. A standard curve is prepared relating color intensity to the concentration of hCG in the sample.