Immunoglobulin G (IgG)

An immunoglobulins test usually measures the three main types of immunoglobulin (Ig) antibodies that your body makes.

IgG is the most common antibody in your blood and provides long-term protection against germs you have already met or been vaccinated against. It is also the only antibody that crosses the placenta from a pregnant person to the baby.

You may need this test if you have symptoms of low immunoglobulin production. One of the main symptoms of low immunoglobulin levels is frequent infections, especially repeated infections from the same germ.

Your provider will compare your levels of IgM, IgG, and IgA. Your results can mean different things, depending on your symptoms, any conditions you may have, and which immunoglobulins are high or low. An immunoglobulins blood test alone cannot diagnose any conditions. So if your results aren't normal, you'll probably need more testing to find out what's affecting your immune system.

Higher than normal IgG may be seen with chronic infections, autoimmune diseases, chronic liver disease, and most often with a plasma cell cancer such as multiple myeloma. A very high IgG driven by a single clone of plasma cells often shows up as a "spike" on a follow-up test called serum protein electrophoresis.

Lower than normal IgG may be a sign of a primary immune deficiency, an effect of medicines that suppress the immune system, kidney problems that lose protein, severe burns, or malnutrition. Low IgG raises the risk of repeated bacterial infections.

If your immunoglobulin levels aren't normal, it doesn't always mean you have a condition that needs treatment. Certain medicines can affect your results. If you have questions about your results, talk with your provider. The earlier you start treating abnormal immunoglobulin levels, the more likely you are to treat its underlying cause.