Immunoglobulin A is second only to lgG in normal human serum, accounting for 10%-20% of serum immunoglobulin content. In terms of structure, lgA is divided into monomeric, bimodal, trimeric and multimodal, and according to its immune function, it is further divided into two types: serotype and secretory type. Low lgA is mainly seen in diseases such as hereditary capillary dilation, non-lgA multiple myeloma, heavy chain disease, light chain disease, malabsorption syndrome, primary disease-free gammoproteinemia, secondary proteinemia, as well as recurrent respiratory infections, transfusion reactions, body immune diseases, nephrotic syndrome, chronic lymphocytic leukemia, Hodgkin’s disease, hereditary thymic hypoplasia, and gammaglobulin abnormal blood, etc.