Low IgG and IgM levels occur with some forms of leukemia, notes WebMD. Low IgG levels alone may occur with macroglobulinemia, a disease that happens when high levels of IgM stop the production of IgG antibodies. Low IgM levels may occur in those diagnosed with multiple myeloma.
Immunoglobulins respond to bacteria, viruses, fungi and other foreign substances that enter the body, according to the American Association for Clinical Chemistry. Low levels of immunoglobulins are mostly caused by conditions that interfere with the production of immunoglobulin or when the body loses a lot of protein. Certain drugs may lower immunoglobulin levels as well. Physicians may test for immunoglobulin levels when a patient exhibits symptoms such as recurring respiratory and gastrointestinal tract infections. The test typically measures different types of immunoglobulin antibodies and helps physicians pinpoint the exact cause of a condition.
IgG antibodies are present in all body fluids, explains WebMD. These antibodies fight bacteria and viruses. They also protect fetuses from infection because they are small enough to cross the placenta. IgM antibodies are the largest type of antibody. Found in blood and lymph fluid, IgM antibodies are the first type of antibodies to respond when foreign substances enter the body. They also spur other antibodies to respond.