IgG, Immunoglobulin G (RDL)

 

What is IgG (Immunoglobulin G)?

Immunoglobulin G (IgG) is the most abundant type of antibody in your blood and body fluids. It plays a central role in your immune system’s defense against infections, especially bacterial and viral pathogens.

IgG antibodies are produced by B cells in response to foreign invaders. Once produced, they help neutralize pathogens, trigger other immune cells to attack, and form long-term immune memory—which is the basis of how vaccines work.

The “RDL” in the test name refers to Rheumatology Diagnostics Laboratory, a specialized lab that often analyzes autoimmune and immunologic markers.

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Why is IgG tested?

An IgG blood test helps evaluate how well your immune system is functioning. It may be ordered to investigate:

• Frequent or severe infections (suggesting immunodeficiency)

• Autoimmune conditions (suggesting overactivity or dysregulation)

• Chronic inflammation

• Monoclonal gammopathies or plasma cell disorders (e.g., multiple myeloma)

• Monitoring after immunoglobulin therapy or bone marrow transplant

It’s also commonly measured alongside IgA and IgM as part of a quantitative immunoglobulin panel.

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What does a high IgG result mean?

An elevated IgG level can indicate that your immune system is overactive or responding to chronic infection, inflammation, or autoimmune disease.

Common causes of elevated IgG include:

1. Chronic Infections

• Tuberculosis

• Chronic hepatitis (especially hepatitis B or C)

• HIV/AIDS (in some phases)

• Fungal or parasitic infections

2. Autoimmune Diseases

• Lupus (SLE)

• Rheumatoid arthritis

• Autoimmune hepatitis

• Sarcoidosis

3. Chronic Inflammation or Immune Activation

• Chronic allergic conditions

• Inflammatory bowel disease (IBD)

• Chronic lung or liver disease

4. Monoclonal or Polyclonal Gammopathies

• Multiple myeloma or MGUS (monoclonal gammopathy of undetermined significance)
  In these cases, IgG may be elevated due to uncontrolled production by abnormal plasma cells.

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What does a low IgG result mean?

A low IgG level may suggest that your immune system can’t produce enough antibodies, leaving you vulnerable to infections.

Possible causes of low IgG include:

1. Primary Immunodeficiencies

• Common Variable Immunodeficiency (CVID)

• X-linked agammaglobulinemia

• Selective IgG subclass deficiency

2. Secondary Immunodeficiencies

• Chronic lymphocytic leukemia (CLL)

• Immunosuppressive therapies (e.g., chemotherapy, corticosteroids)

• Nephrotic syndrome (IgG lost in urine)

• Protein-losing enteropathy

• Bone marrow failure or transplant

People with low IgG often have frequent respiratory infections, chronic sinusitis, or pneumonia and may require immunoglobulin replacement therapy (IVIG or SCIG).

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What does a normal IgG result mean?

A normal IgG level suggests your immune system is producing antibodies appropriately and there’s no current evidence of a major immune deficiency or hyperactivity.

However, normal levels don’t always rule out disease—clinical symptoms and other lab findings are essential to the full picture.

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What happens next if your IgG is abnormal?

If IgG is elevated:

• Your doctor may order additional testing, such as:

  • IgA, IgM, and IgE levels

  • Autoimmune panels (ANA, RF, dsDNA)

  • Protein electrophoresis (SPEP/UPEP) to detect monoclonal spikes

  • Infectious disease screening

• You may be referred to a rheumatologist, infectious disease specialist, or hematologist

If IgG is low:

• Your provider may:

  • Order IgG subclass testing

  • Evaluate your infection history

  • Consider immunoglobulin replacement therapy if infections are frequent

  • Refer you to an immunologist

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Bottom Line

IgG (Immunoglobulin G) is a vital part of your immune defense system. Abnormal levels—either too high or too low—can be a sign of chronic infection, autoimmune activity, immune deficiency, or other systemic conditions. Whether you're experiencing frequent infections or unexplained inflammation, this test offers critical insight into how your immune system is functioning and what steps may be needed next.