Immunoglobulin G (IgG)
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 " 43Normal Ranges for IgG by AgeView LargeTABLE 16 " 43Normal Ranges for IgG by Age Age Range (mg/dL) 0 " 30 d 611 " 1,542 1 m 241 " 870 2 mo 198 " 577 3 mo 169 " 558 4 mo 188 " 536 5 mo 165 " 781 6 mo 206 " 676 7 " 8 mo 208 " 868 9 " 11 mo 282 " 1,026 1 y 331 " 1,164 2 y 407 " 1,009 3 y 423 " 1,090 4 y 444 " 1,187 5 " 7 y 608 " 1,229 8 " 9 y 584 " 1,509 ≥10 y 768 " 1,632
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
- Waldenstr śm 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