IgG

Overview

IgG measures the concentration of immunoglobulin G, the most abundant antibody class in human serum, which is produced by B cells and plasma cells in response to antigen exposure. As the major circulating immunoglobulin, IgG provides long‑term humoral immunity by neutralizing pathogens, promoting opsonization, and activating complement. Low total IgG levels suggest humoral immunodeficiency (e.g., common variable immunodeficiency), whereas high levels may indicate chronic infections, autoimmune disorders, or polyclonal gammopathies. Clinically, IgG measurement is used to evaluate immunologic status, screen for immune deficiency, and help characterize lymphoproliferative and autoimmune conditions.

Clinical Use Cases

  • Evaluating suspected primary immunodeficiency (e.g., hypogammaglobulinemia, common variable immunodeficiency).
  • Monitoring antibody replacement therapy with intravenous immunoglobulin (IVIG).
  • Investigating chronic infections and autoimmune diseases associated with polyclonal IgG elevation.
  • Supporting workup of monoclonal gammopathies when combined with serum protein electrophoresis (SPEP) and free light‑chain assays.

Specimen Types

  • Serum (most common specimen for IgG quantification).
  • Plasma (less commonly used; serum is standard for immunoglobulin assays).

Measurement Methods

  • Nephelometry (automated, most widely used in clinical labs).
  • Turbidimetry (immunoturbidimetric assays on chemistry analyzers).
  • ELISA or radial immunodiffusion (used more in research or specialized reference settings).

Test Preparation and Influencing Factors

  • No special fasting requirement, but consistent timing and specimen handling are recommended.
  • IVIG infusion or recent blood transfusion can transiently elevate serum IgG.
  • Chronic infections, autoimmune diseases, and some malignancies cause polyclonal increases, while protein‑losing states or nephrotic syndrome may lower IgG.
  • Age, chronic illness, and immunosuppressive treatments can influence baseline IgG levels.

Synonyms

  • Immunoglobulin G.
  • IgG, serum.
  • Gamma‑globulin G (older, less precise term).

Further Reading