Immunoglobulin G (IgG) is the most abundant antibody in the bloodstream, making up roughly 75% of total serum immunoglobulins. It is the main antibody responsible for long-term immune memory. After you recover from an infection or receive a vaccine, IgG antibodies persist in your blood and provide ongoing protection against reinfection.
Low total IgG (hypogammaglobulinaemia) suggests that the body is not producing enough antibodies. This can be primary, as in common variable immunodeficiency (CVID), or secondary, caused by medications such as corticosteroids, chemotherapy, or haematological conditions. People with significantly low IgG tend to experience recurrent bacterial infections, particularly of the respiratory and gastrointestinal tracts.
Elevated IgG has a different set of implications. It can reflect chronic immune stimulation from autoimmune disease, chronic viral infections such as hepatitis, or liver conditions including cirrhosis. Very high IgG may also indicate a monoclonal or polyclonal gammopathy. If IgG is markedly elevated, your practitioner may order protein electrophoresis and immunofixation to look for an abnormal clonal antibody.
IgG is most informative when measured as part of a full immunoglobulin panel alongside IgA and IgM. Together, these three markers give a comprehensive view of humoral immune function. If a subclass deficiency is suspected (where total IgG is normal but one of the four IgG subclasses is low), separate IgG subclass testing can be arranged.
This test is commonly ordered for people with recurrent infections, unexplained fatigue with immune concerns, or as part of a broader immunology workup. Your practitioner will interpret the result alongside your clinical history and other investigations.
To assess immunoglobulin G levels as a marker of humoral immune function, and to investigate conditions associated with abnormally low or high antibody production.
