Immunoglobulin G (IgG) in Serum or Plasma by Immunoassay

What Is Immunoglobulin G (IgG)?

IgG is the most common type of antibody in your blood. Antibodies are proteins that help your immune system recognize and fight off harmful substances like bacteria and viruses. IgG is particularly important because it can cross the placenta, providing passive immunity to a newborn. Your body produces IgG in response to infections or vaccines, helping you build long-term immunity.

Why Might You Need This Test?

Doctors may order an IgG test to diagnose or monitor conditions such as immune deficiencies, infections, autoimmune diseases, or to check for antibodies in a newborn’s blood. It can also help evaluate how well a person’s immune system is responding to treatment.

Common Uses of IgG Testing

IgG testing is commonly used in pediatric care to assess newborn immunity, in adults to diagnose conditions like HIV, lupus, or chronic infections, and in research or clinical trials to measure antibody levels in response to vaccines or treatments.

What to Expect Before the Test

No special preparation is usually needed for this test. You may have a small needle inserted into your arm or vein to draw blood. If you’re a child or have a hard time staying still, your doctor or nurse may use a smaller needle or a special device to collect blood more easily.