Immunoglobulin M

Test ID: 


CPT code:



Immunoglobulin M, Quantitative

IgM, Serum

Quantitative IgM, Serum

Clinical Use:

Evaluate humoral immunity; establish the diagnosis and monitor therapy in macroglobulinemia of Waldenström or plasma cell myeloma. IgM levels are used to evaluate likelihood of in utero infections or acuteness of infection.

Test Information:

Immunoglobulin M is a pentamer of 7S γ-globulin and is an efficient complement binder. It is the antibody type produced initially in the immune response and the first immunoglobulin class to be synthesized by a fetus or newborn. IgM antibodies do not cross the placenta. For these reasons the demonstration of IgM-specific antibody is useful in assessing whether a particular infection is acute (in which case IgM antibodies will be present) or chronic (IgG antibodies will predominate) and whether a newborn has a congenital infection (a newborn with IgM antibody is infected; a newborn with IgG antibody has passively acquired maternal antibody, which simply crossed the placenta). In the hyper-IgM immunodeficiency syndrome, there is an absence of IgG and IgA in serum and a marked increase in IgM. Macroglobulins produced in Waldenström disease are IgM, and may produce hyperviscosity syndrome. More than 2 g/dL of monoclonal IgM is a major diagnostic criterion of myeloma. Increased IgM (with other immunoglobulins) may develop in inflammatory/infectious conditions. IgM is characteristically elevated in primary biliary cirrhosis. The majority of rheumatoid factors are IgM. IgM will be decreased in congenital or acquired hypogammaglobulinemia, and this will be associated with increased, recurrent infection.

Specimen Type:


Requested Volume: 

1 mL (adult), 0.4 mL (pediatric)

Minimum Volume: 

0.4 mL

Container Type: 

Red-top tube or gel-barrier tube

Storage Instructions:

Samples suspected of having macroglobulins or cryoglobulins should be drawn and held at 37°C. Samples suspected of containing cold agglutinins should not be refrigerated prior to serum separation from clot.

Stability Requirements:



Room temperature

14 days


14 days


14 days

Freeze/thaw cycles

Stable x3

Rejection Criteria:

Excessive lipemia

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Sun: 7AM-3PM

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