Immunoglobulin M (IgM), Serum/Plasma

Immunoglobulin M (IgM) is by far the largest antibody in the human circulatory system because it forms polymers where multiple immunoglobulins are covalently linked together as a pentamer but also as a hexamer. Because IgM is a large molecule, it cannot diffuse well, and is found in the interstitium only in very low quantities, thus, IgM is primarily found in serum. Due to its polymeric nature, IgM possesses high avidity, and is particularly effective at complement activation. Another characteristic of , is that it is the primary naturally occuring antibody against A and B antigens on red blood cells.

IgM antibodies appear early in the course of an infection and usually reappear, to a less extent, after further exposure. IgM antibodies do not pass across the human placenta. These two biological properties of IgM make it useful in the diagnosis of infectious diseases. Demonstrating IgM antibodies in a patient’s serum indicates recent infection. Polyclonal increase in serum IgM is normal in response to infections as well as mononucleosis, rheumatoid arthritis and malaria. Monoclonal increase in serum IgM occurs in Waldenstrom’s macroglobulinemia, malignant lymphoma, reticulosis and in monoclonal cryoglobulinemias. Decreased levels are very rare and associated with recurrent pyogenic infections. Secondary deficiency is seen in association with multiple myeloma (IgA or IgG) and protein losing enteropathy, but not with nephrotic syndrome.

1 ml Serum 1 ml Li, Na-Heparin or Na2, K3-EDTA Plasma Stability: 2 Months at 15-25 °C 4 Months at 2-8 °C 6 Months at (-15)-(-25) °C

< 1 yr: 0 - 145 mg/dL 0.00 - 1.45 g/L 1-3 yrs: 19 - 146 mg/dL 0.19 - 1.46 g/L 4-6 yrs: 24 - 210 mg/dL 0.24 - 2.10 g/L 7-9 yrs: 31 - 208 mg/dL 0.31 - 2.08 g/L 10-11 yrs: 31 - 179 mg/dL 0.31 - 1.79 g/L 12-13 yrs: 35 - 239 mg/dL 0.35 - 2.39 g/L 14-15 yrs: 15 - 188 mg/dL 0.15 - 1.88 g/L 16-19 yrs: 23 - 259 mg/dL 0.23 - 2.59 g/L > 19 yrs: 40 - 230 mg/dL 0.40 - 2.30 g/L