Immunoglobulin A (IgA), serum

The Immunoglobulin A (IgA), serum test—also referred to as Total IgA or Serum IgA—is used to appraise humoral immunity and to identify selective or combined IgA deficiency. It is ordered in the assessment of patients with recurrent sinopulmonary, gastrointestinal, or urogenital infections. Serial IgA measurements aid in monitoring IgA-type multiple myeloma and immune dysregulation associated with autoimmune and hematologic disorders. The assay also contributes to comprehensive immune status evaluation.

IgA is synthesized predominantly by plasma cells in mucosal tissues in response to local antigen exposure. In humans, it occurs as a monomer in serum and as a dimeric secretory form; the serum half-life is approximately 6–7 days. In blood, 80%–90% of IgA circulates as the monomer, and overall IgA constitutes about 10%–15% of total immunoglobulins. The secretory dimer is present in tears, sweat, saliva, breast milk, and in respiratory and gastrointestinal secretions. This form is relatively resistant to proteolysis and protects mucosal surfaces by neutralizing pathogens, limiting microbial translocation, activating complement via the alternative pathway, and promoting phagocytosis. Selective IgA deficiency is among the most common primary immunodeficiencies (approximately 1:400–1:700). Many individuals are asymptomatic, but associations include atopy, recurrent respiratory or gastrointestinal infections, and autoimmune diseases such as type 1 diabetes, systemic lupus erythematosus, rheumatoid arthritis, and pernicious anemia. Concomitant reductions in IgG2 and IgG4 may yield a more pronounced clinical immunodeficiency phenotype. Individuals with congenital IgA deficiency have an increased risk of forming anti-IgA antibodies, which can trigger anaphylactic reactions during transfusion of blood components or administration of intravenous immunoglobulin.