The Calbiotech Secretory IgA (sIgA) kit is a solid phase direct ELISA sandwich method. The standards, samples and controls are added into designated wells, coated with anti-sIgA monoclonal antibody, along with the incubation buffer. After a simple washing step, an anti-SIgA enzyme conjugate reagent is added into each well. After the excess enzyme conjugate is washed out, a chromogenic substrate (TMB) is added into each well. Upon the addition of the substrate, the intensity of color developed is directly proportional to the concentration of sIgA in the samples. A standard curve is generated relating color intensity to the concentration of sIgA.