Immunoglobulin A is an antibody that plays a role in the immune function of mucous membranes. In normal serum, about 15% is IgA. To diagnose a variety of conditions, including: Bacterial or viral infections. Immunodeficiency, a condition that reduces the bodys ability to fight infections and other diseases. An autoimmune disorder, such as rheumatoid arthritis or lupus. High immunoglobulin level, might cause Allergies, Chronic infections. Increased serum immunoglobulin concentrations occur due to polyclonal or oligoclonal immunoglobulin proliferation in hepatic disease (hepatitis, liver cirrhosis), connective tissue diseases, acute and chronic infections, as well as in the cord blood of neonates with intrauterine and perinatal infections.Elevation of IgA may occur in monoclonal gammopathies such as multiple myeloma, primary systemic amyloidosis, monoclonal gammopathy of undetermined significance, and related disorders. Decreased levels are found in patients with primary or secondary immune deficiencies.