Immunoglobulin G (IgG) in Serum

What Does IgG Measure?

IgG is the primary antibody your immune system produces in response to infections, vaccines, and chronic illnesses. It circulates in your bloodstream and provides long-lasting protection against pathogens like bacteria and viruses. This test helps assess your immune system’s ability to defend against these threats.

Why Might You Need This Test?

Doctors may order an IgG test to evaluate immune function, diagnose conditions like immunodeficiency, monitor treatment responses for autoimmune diseases, or check for infections where IgG levels might be abnormal.

Common Reasons for Testing

Common reasons include identifying immune deficiencies (e.g., HIV, certain genetic disorders), assessing vaccine responses, diagnosing autoimmune diseases (e.g., lupus, rheumatoid arthritis), or evaluating chronic infections (e.g., tuberculosis, hepatitis). It may also be used in newborn screening or before certain medical procedures.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if it involves a blood draw. Wear comfortable clothing and inform your doctor about any medications or conditions that could affect results.