Immunoglobulin M (IgM)

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 " 44Normal Ranges for IgM by AgeView LargeTABLE 16 " 44Normal Ranges for IgM by Age Age Range (mg/dL) 0 " 30 d 0 " 24 1 mo 19 " 83 2 mo 16 " 100 3 mo 23 " 85 4 mo 26 " 96 5 mo 31 " 103 6 mo 33 " 97 7 " 8 mo 32 " 120 9 " 11 mo 39 " 142 1 y 41 " 164 2 y 46 " 160 3 y 45 " 190 4 y 41 " 186 5 " 7 y 46 " 197 8 " 9 y 49 " 230 ≥10 y 60 " 263

Use

• Diagnosis of hereditary and acquired IgM immunodeficiencies
• Diagnosis of Waldenstr śm macroglobulinemia
• Earliest Ig serologic diagnosis of infectious disease

Interpretation

Increased In

• Polyclonal Liver disease Chronic infections Secondary to nephritic syndrome Hyper IgM syndrome
• Monoclonal Waldenstr śm 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.