Immunoglobulin A (IgA) is the most abundant antibody class in the human body when you include the amounts produced at mucosal surfaces. While IgG dominates in the bloodstream, IgA is the primary antibody lining the gut, respiratory tract, and urogenital system. It acts as a first-line barrier, neutralising pathogens and toxins before they can cross into deeper tissues.
Serum IgA, the form measured in this blood test, reflects the circulating pool rather than the mucosal compartment. Low serum IgA is the hallmark of selective IgA deficiency, the most common primary immunodeficiency in Australia, affecting roughly 1 in 500 people. Many individuals with IgA deficiency are entirely asymptomatic. Others experience recurrent respiratory infections, gastrointestinal symptoms, or allergic conditions.
One of the most practical reasons for measuring IgA is its relationship with coeliac disease testing. Standard coeliac antibody tests (anti-tTG IgA) rely on the patient being able to produce IgA. If IgA is deficient, these tests can return a false-negative result even in the presence of active coeliac disease. Knowing your IgA status before or alongside coeliac testing ensures the right antibody tests are ordered.
Elevated IgA can occur in chronic infections, autoimmune conditions such as IgA nephropathy (Berger's disease), liver disease including cirrhosis, and rarely in IgA myeloma. The clinical significance depends on the degree of elevation and the broader clinical picture.
This test is typically ordered as part of an immunoglobulin panel (alongside IgG and IgM) or specifically to validate coeliac disease antibody testing. Your practitioner will interpret the result in the context of your symptoms, medical history, and other laboratory findings.
To screen for IgA deficiency before coeliac antibody testing, investigate recurrent infections affecting the gut or respiratory tract, and assess mucosal immune function as part of an immunology workup.
