IgG Subclass 4

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. IgG4 is the smallest subclass (about 4% of total IgG), and unlike the others, it does not strongly activate the complement system. A high IgG4 level can be a clue to a condition called IgG4-related disease, in which IgG4-producing immune cells build up in organs such as the pancreas, salivary glands, kidneys, or lungs.

You may need this test if you have symptoms of low immunoglobulin production, or if your provider is checking for IgG4-related disease.

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.

A high IgG4 level fits with - but does not by itself prove - IgG4-related disease. A diagnosis usually also needs a typical pattern on imaging and on a tissue biopsy. IgG4 can also be high with some allergic conditions or after long-term exposure to certain antigens.

An isolated low IgG4 is common and is often not a sign of an immune problem on its own.

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.