Serum or plasma concentration of immunoglobulin G (IgG) by immunoassay

What Is Immunoglobulin G (IgG)?

IgG is the most common type of antibody in your blood. It plays a key role in fighting off infections, including bacteria and viruses. Your body produces IgG to help remember past infections and provide long-term protection. Low levels of IgG can indicate a weakened immune system, while high levels may suggest certain immune-related conditions or overproduction.

Why Might You Need This Test?

Your doctor may order an IgG test if you have symptoms of an immune disorder, such as frequent infections, recurrent colds, or slow healing of wounds. It may also be used to monitor immune function in people with conditions like HIV, lupus, or other autoimmune diseases, or after treatments like chemotherapy that affect immunity.

Common Reasons for Testing

Common reasons include diagnosing immune deficiencies, evaluating symptoms of chronic infections, assessing response to treatments for autoimmune diseases, or checking for conditions like common variable immunodeficiency (CVID). It can also be part of a broader workup for unexplained infections or developmental delays in children.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the test if your blood is drawn early in the morning. Wear a loose shirt for easy access to your arm. If you’re on blood thinners, let your doctor know before the test.