IgG Subclass 3

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. It is made up of four subclasses called IgG1, IgG2, IgG3, and IgG4. IgG3 is a small part of total IgG (about 5-7%) but is one of the strongest at activating other parts of the immune system, such as the complement system, and it plays an important role in fighting many viral infections. IgG3 has a shorter life in the blood (about a week) than the other IgG subclasses.

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.

An isolated low IgG3 in someone without infections is often not clearly important. When low IgG3 occurs along with low levels of other immunoglobulins (such as in common variable immunodeficiency), it can be part of a wider immune deficiency.

Higher than normal IgG3 is usually not specific. It can be seen with chronic infections or inflammatory and autoimmune diseases.

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.