IgG (immunoglobulin G) is the most abundant antibody in blood, accounting for about 75% of all serum immunoglobulins. It is the primary antibody of long-term immune memory, produced by plasma cells following exposure to pathogens or vaccination. IgG provides sustained protection against repeat infections and is the only immunoglobulin class that crosses the placenta to protect newborns.
IgG exists in four subclasses (IgG1-4) with distinct structural properties and biological functions. Total IgG measurement reflects the aggregate of these subclasses. Elevated IgG is common in chronic infections, autoimmune conditions, and liver disease. Low IgG indicates humoral immunodeficiency and increased susceptibility to bacterial infections. IgG is also the class targeted in passive immunotherapy with IVIG (intravenous immunoglobulin).
FAQs
What does IgG measure?
IgG measures the total amount of the most abundant antibody class in your blood, which provides long-term immune memory. High IgG indicates active or prior immune stimulation; low IgG indicates reduced immune protection.
What is common variable immunodeficiency (CVID)?
CVID is the most common primary antibody deficiency, characterised by low IgG (and often low IgA and IgM), poor vaccine responses, and recurrent bacterial respiratory infections. It is managed with regular IgG replacement therapy.
What is IVIG and who needs it?
IVIG (intravenous immunoglobulin) is pooled IgG from thousands of blood donors given by infusion to people with immunodeficiency (CVID), autoimmune conditions, and certain inflammatory diseases. It replaces absent IgG or modulates immune responses depending on the indication.
How is IgG myeloma diagnosed?
IgG myeloma is diagnosed by protein electrophoresis showing a monoclonal IgG band, confirmed by immunofixation. Further evaluation includes bone marrow biopsy showing plasma cell infiltration, skeletal survey or PET-CT for bone lesions, and assessment of organ damage.
