Immunoglobulin M (IgM)

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

IgM is the first antibody your body makes when it meets a new germ, so a high IgM can sometimes point to a recent or new infection. Later, your body switches to making mostly IgG against that germ.

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.

Some possible causes of low levels of one or more immunoglobulins are kidney disease, serious burns, malabsorption disorders, malnutrition, or a genetic immunodeficiency disorder.

Higher than normal IgM may be seen in early infections, chronic liver disease, and autoimmune diseases. A very high IgM coming from a single clone of cells may point to Waldenstrom macroglobulinemia or a related blood disorder, and usually leads to extra tests such as serum protein electrophoresis or a bone marrow exam.

Some possible causes of high levels of one or more immunoglobulins are autoimmune disease, hepatitis, cirrhosis, chronic infections, or cancers such as multiple myeloma or lymphoma.

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.