Immunoglobulin M (IgM)
IgM normally consists of 10 heavy μ‑chains and 10 kappa or lambda type light chains which are always identical within a molecule. There is also a J‑chain linking all the μ‑chains together, so that simply speaking, IgM has a pentameric structure when compared to that of IgG. IgM is the largest immunoglobulin molecule (MW = 970000), but makes up only 6 % of the plasma immunoglobulins.
IgM is the first specific antibody to appear in the serum after infection. It is capable of activating complement, thus helping to kill bacteria. After the infection has subsided, IgM levels sink at a relatively rapid rate compared to IgG. This fact is used to advantage in the differential diagnosis of acute and chronic infections by comparing specific IgM and IgG titers. If IgM is prevalent the infection is acute, whereas if IgG predominates the infection is chronic (e.g. rubella, viral hepatitis). Increased polyclonal IgM levels are found in viral, bacterial, and parasitic infections, liver diseases, rheumatoid arthritis, scleroderma, cystic fibrosis and heroin addiction. Monoclonal IgM is increased in Waldenström’s macroglobulinemia. Increased loss of IgM is found in protein‑losing enteropathies and in burns. Decreased synthesis of IgM occurs in congenital and acquired immunodeficiency syndromes. Due to the slow onset of IgM synthesis, the IgM concentration in serum of infants is lower than in adults.
SI units Conversion Calculator. Convert Immunoglobulin M (IgM) level to mmol/L, µmol/L, g/L, mg/dL, mg/100mL, mg%, mg/mL. Clinical laboratory units online conversion from conventional or traditional units to Si units. Table of conversion factors for Immunoglobulin M (IgM) unit conversion to mmol/L, µmol/L, g/L, mg/dL, mg/100mL, mg%, mg/mL.