IgG Subclass 1

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 is made up of four "subclasses" called IgG1, IgG2, IgG3, and IgG4. IgG1 is the largest subclass - about 60-65% of total IgG - and is your main antibody for fighting many bacterial and viral infections. IgG1 also crosses the placenta to help protect babies during the first months of life.

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.

A low IgG1 level is most often part of a wider antibody deficiency such as common variable immunodeficiency or combined immunodeficiency, since IgG1 makes up most of your IgG. Truly isolated low IgG1 is uncommon. A small dip below the normal range without symptoms or repeated infections is usually not a problem.

Higher than normal IgG1 may be seen with chronic infections, autoimmune diseases, chronic liver disease, or some plasma cell disorders.

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.