IgA (Immunoglobulin A)

IgA (Immunoglobulin A) is the most abundant antibody class produced by the body and serves as the principal defender of mucosal surfaces, including the respiratory tract, gastrointestinal lining, and genitourinary system. This test measures the total concentration of IgA in a simple blood sample, typically using an immunoturbidimetric or ELISA-based analytical method, to assess whether the immune system is producing this antibody at an appropriate level.

Clinicians request an IgA test for several reasons. It may be used to investigate recurrent respiratory or gastrointestinal infections, to screen for conditions associated with abnormal immunoglobulin production, or as part of a broader immunological workup. It is also commonly ordered alongside other immunoglobulin tests (IgG and IgM) to build a complete picture of humoral immune function. In coeliac disease assessment, total IgA is measured first to ensure that a subsequent tissue transglutaminase (tTG) IgA result is interpretable, since IgA deficiency can cause a false negative.

What is measured

• Total IgA: The overall concentration of immunoglobulin A in the bloodstream. IgA exists in two main forms: serum IgA, which circulates in the blood, and secretory IgA, which is found in mucosal secretions such as saliva, tears, and intestinal fluid. This test measures the serum fraction.

Why it matters

IgA plays a unique and essential role in immune defence. Unlike other antibodies that primarily circulate in the blood, IgA is concentrated at mucosal barriers where the body meets the outside world. Abnormal IgA levels can indicate underlying immune dysfunction, chronic infection, autoimmune conditions, or, in rare cases, haematological disorders. Identifying an IgA deficiency is particularly important before interpreting coeliac serology, and low or absent IgA can explain a pattern of repeated infections. Conversely, elevated IgA may be seen in chronic liver disease, inflammatory conditions, or certain infections. Measuring IgA gives your clinician a vital piece of the immune puzzle, guiding further investigation and helping to ensure that other test results are interpreted correctly.

• Immunoglobulin A (IgA)

No special preparation required.

For blood tests, we recommend drinking plenty of water beforehand to ensure smooth sample collection. If you are taking any regular medication, continue to do so unless advised otherwise by your doctor.