Immunoglobulin G Blood Test

Note: This test measures total Immunoglobulin G (IgG) levels only and does not include IgG subclass analysis.

What is the purpose of this test?

Order this Immunoglobulin G (IgG) Blood Test, QN, to measure the blood's immunoglobulin G (IgG) levels to assess the immune system status and detect or monitor a deficiency or excess. Immunoglobulins, commonly known as antibodies, are vital to the body's immune system. These immunoglobulins are proteins produced by plasma cells in the immune system as a response to harmful antigens (bacteria or viruses) that cause infections or illnesses. 

When an individual becomes infected or exposed to an antigen, their immune system recognizes the microorganism or substance as foreign. As a result, it stimulates the plasma cells to produce specific immunoglobulins (antibodies) that combat the invaders. Suppose the individual is exposed to the antigen again. In that case, the immune system "recognizes" the antigen encountered, which allows for the immediate production of more antibodies to help stop re-infection.

What does this test measure?

This Immunoglobulin Blood Test screens one of the most common immunoglobulins, IgG. This immunoglobulin type represents a specific group of antibodies with a special function. This test screens for the following immunoglobulin:

• Immunoglobulin G (IgG) – IgG is the most abundant immunoglobulin found in the blood and plays a critical role in the body's long-term immune response. IgG antibodies are produced following exposure to infections, vaccines, or other foreign substances (antigens). Levels typically rise during an immune response and may remain elevated for an extended period to help provide future protection.

  This test measures the total amount of Immunoglobulin G (IgG) in the blood. It does not measure or report the individual IgG subclasses (IgG1, IgG2, IgG3, and IgG4).

What causes an immunoglobulin G deficiency or excess?

Individuals may acquire an immunoglobulin G deficiency through an underlying condition, usage of certain medications, or other contributing factors that prevent immunoglobulin production. In addition, a deficiency may be inherited through a rare genetic disorder. The following conditions are associated with an immunoglobulin G deficiency:

• Kidney disease
• Diabetes
• Nephrotic syndrome
• Usage of immunosuppressant drugs, phenytoin, and carbamazepine
• Short-term developmental delay in premature infants
• Gastrointestinal issues that affect digestion or absorption of proteins

However, an individual may also experience excessive IgG levels (monoclonal increase) due to several conditions. The following conditions are related to excessive IgG levels:

• Acute or chronic infections
• Autoimmune disorders
• Cirrhosis
• Inflammatory disorders
• Hyperimmunization reactions
• Wiskott-Aldrich syndrome
• Congenital infection (syphilis, toxoplasmosis, rubella, CMV)
• Multiple myeloma
• Chronic lymphocytic leukemia (CLL)
• MGUS (monoclonal gammopathy of undetermined significance)
• Lymphoma
• Waldenstrom's macroglobulinemia