This human IgA ELISA Kit is suitable for qualitatively determining human IgA concentrations in the serum and plasma in vitro. IgA makes up more than two-thirds of the total immunoglobulin produced by the body. IgA acts as a first-line barrier, preventing intestinal antigens from reaching the gut mucosa, regulating the intestinal microbiota, and dampening pro-inflammatory immune responses. IgA also removes pathogens or antigens by an IgA-mediated excretory pathway, in which immune complexes are bound to IgA and then transported by polyimmunoglobulin receptors. At mucosal surfaces, secretory IgA plays a key role in mediating adaptive humoral immune defense. This kit uses the quantitative sandwich-based enzyme immunoassay technique to measure the amount of human IgA in the sample. Standards and samples are respectively added to the microplate wells pre-coated with an anti-human IgA antibody. Biotin-labeled IgA antibody, HRP-avidin, and TMB substrate are pipped into the microplate in turn. The capture antibody pre-coated on the plate captures the IgA in the rat samples. IgA binds to the biotinylated anti-IgA human monoclonal antibody. And the biotin on the biotinylated anti-IgA human monoclonal antibody binds to the avidin on the enzyme label, forming immune complexes. The color renders blue after the addition of the TMB substrate. The addition of the stop solution into the wells immediately turns the blue into yellow. The concentration of IgA in the samples is directly proportional to OD (450nm). Each manufactured lot of this ELISA kit was quality tested for criteria such as sensitivity, specificity, precision, linearity, and lot-to-lot consistency.