Immunoglobulin G (IgG)

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Subject: Immunoglobulin G (IgG)

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Definition

  • IgG activates complement and fights infection. IgG represents 70–80% of the total serum immunoglobulins in the normal adults. It exists in four subclasses (IgG1, IgG2, IgG3, and IgG4). IgG1 predominates as 65% of the total IgG. IgG of maternal origin provides passive immunity to the neonate. It is transported across the placenta.

  • Normal ranges: see Table 16.43.

 
TABLE 16–43
Normal Ranges for IgG by Age

Use

  • Diagnosis of IgG myeloma

  • Diagnosis of hereditary and acquired IgG immunodeficiencies

  • Serologic diagnosis of infectious diseases and immunity

Interpretation

Increased In

  • Monoclonal

    • Multiple myeloma

    • Solitary plasmacytoma

    • MGUS

    • Lymphoma

    • CLL

  • Polyclonal

    • Sarcoidosis

    • Chronic liver disease (e.g., cirrhosis)

    • Autoimmune diseases

    • Parasitic diseases

    • Chronic infection

    • Intrauterine contraceptive diseases

Decreased In

  • Protein-losing syndromes

  • Pregnancy

  • Non-IgG myeloma

  • Waldenström macroglobulinemia

  • Primary immunodeficiency states

  • Combined with other immunoglobulin decreases:

    • Agammaglobulinemia

      • Acquired

      • Primary

      • Secondary (e.g., multiple myeloma, leukemia, nephrotic syndrome, protein-losing enteropathy)

      • Congenital

      • Hereditary thymic aplasia

      • Type I dysgammaglobulinemia (decreased IgG and IgA and increased IgM)

      • Type II dysgammaglobulinemia (absent IgA and IgM and normal levels of IgG)

      • Infancy, early childhood

 
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