Serum Immunoglobulin G (IgG) Level

What Does This Test 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 broad protection against pathogens like bacteria and viruses. Low levels may indicate immune deficiencies, while high levels can sometimes suggest chronic infections, autoimmune conditions, or overactive immune responses.

Why Might You Need This Test?

Your doctor may order an IgG test if you have symptoms of weakened immunity (e.g., frequent infections, slow wound healing), a history of severe illnesses, or if you’re being evaluated for conditions like HIV, lupus, or certain autoimmune diseases. It’s also used to monitor immune responses after vaccination or treatment for infections.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the blood draw if your lab requires it. Wear a loose shirt for easy access, and inform your doctor about any medications or supplements you take, as they could affect results.

What Happens During the Test?

A healthcare provider will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but the procedure usually takes just a few minutes. The blood sample is then sent to a lab for analysis.