Immunoglobulin A (IgA) is the most abundant antibody in mucosal secretions — found in saliva, tears, breast milk, and the lining of the respiratory and gastrointestinal tracts. It serves as the first line of immune defence at these mucosal surfaces, preventing pathogens from adhering and penetrating tissues. Serum IgA reflects the systemic pool of this antibody class.
Elevated serum IgA can indicate chronic mucosal infection, liver disease (particularly alcoholic liver disease), autoimmune conditions such as IgA nephropathy, and certain malignancies including IgA myeloma. Low IgA (IgA deficiency) is the most common primary immunodeficiency, affecting approximately 1 in 600 people, and increases susceptibility to respiratory and gastrointestinal infections. IgA deficiency also causes false-negative results on tTG-IgA coeliac disease tests.
FAQs
Why is IgA measured before coeliac testing?
The standard coeliac blood test (tTG-IgA) relies on IgA antibodies. In IgA-deficient individuals, this test gives a false-negative result even if coeliac disease is present. Measuring total IgA alongside tTG-IgA allows identification of IgA-deficient patients who need alternative testing.
What is IgA nephropathy?
IgA nephropathy (Berger's disease) is the most common primary glomerulonephritis worldwide, caused by IgA immune complex deposition in the kidney. It presents with haematuria, proteinuria, and sometimes hypertension. Serum IgA is elevated in about 50% of cases.
Is IgA deficiency serious?
Most people with IgA deficiency are asymptomatic or have only mildly increased infection susceptibility. However, IgA deficiency is associated with increased risk of autoimmune diseases and anaphylactic reactions to blood products containing IgA.
What is IgA myeloma?
IgA myeloma is a plasma cell cancer producing a monoclonal IgA paraprotein. It causes markedly elevated IgA, bone pain, anaemia, kidney impairment, and recurrent infections. Diagnosis requires protein electrophoresis, bone marrow biopsy, and imaging.
