Immunoglobulin M (IgM)

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Subject: Immunoglobulin M (IgM)

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Definition

  • IgM is the first antibody to appear in response to antigen. It can be produced by the fetus and cannot be crossed by the placenta.

  • Normal range: see Table 16.44.

 
TABLE 16–44
Normal Ranges for IgM by Age

Use

  • Diagnosis of hereditary and acquired IgM immunodeficiencies

  • Diagnosis of Waldenström macroglobulinemia

  • Earliest Ig serologic diagnosis of infectious disease

Interpretation

Increased In

  • Polyclonal

    • Liver disease

    • Chronic infections

    • Secondary to nephritic syndrome

    • Hyper IgM syndrome

  • Monoclonal

    • Waldenström macroglobulinemia

    • Lymphoma

    • CLL

    • Multiple myeloma (rare)

    • Schnitzler syndrome

    • Cold IgM antibody agglutinin

    • MGUS

Decreased In

  • Protein-losing syndromes

  • Non-IgM myeloma

  • Infancy, early childhood

Limitations

  • Selective deficiency of IgM is a rare immune disorder in association with infection and normal levels of other immunoglobulin isotypes.

 
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