Clinical Information

Immunoglobulin M (IgM) is the first immunoglobulin synthesized during an immune response. It presents as a pentamer that enables direct cross-linking and agglutination of particulate and cellular antigens. Antigen-IgM complexes actively fix complement. Since IgM is produced during an initial immune response, it is useful in differentiating between an acute infection (IgM present) or a chronic infection (IgG present).

Viral infections like viral hepatitis or infectious mononucleosis, and early bacterial or parasitic infections may increase polyclonal IgM. IgM levels can also be increased in rheumatoid arthritis, chronic hepatocellular disease and other chronic disorders. Hyper-IgM dysgammaglobulinemia, active sarcoidosis, collagen vascular disease and nephrotic syndrome will also have elevated levels of IgM. Monoclonal IgM increases can be seen in Waldenstrom’s macroglobulinemia, malignant lymphoma, reticulosis and cold agglutinin hemolysis disease. Decreased levels of IgM are primarily a secondary deficiency due to an IgA or IgG type multiple myeloma, protein losing enteropathies, burns, or immunosuppressive therapy. Increased recurrent infections are also associated with IgM deficiencies.