IgG Test

Immunoglobulin G (IgG) is the most abundant antibody in your bloodstream and a key part of your immune defense. Antibodies are proteins made by your immune system to recognize and neutralize harmful invaders like viruses, bacteria, and toxins. IgG stands out because it not only fights off infections when they happen—it also helps your body remember past infections so you can respond faster next time.

IgG is the only antibody that can cross the placenta from mother to baby, providing protection in the first weeks of life. It also circulates easily between the blood and tissues, making it especially useful for detecting and responding to threats throughout the body. Over time, IgG helps keep inflammation in check, clears out dead or damaged cells, and fine-tunes the immune response so it doesn’t overreact.

Because it plays such a central role in immunity, your IgG level can serve as a window into your immune system’s overall status.

When IgG Is High or Low

Low IgG (hypogammaglobulinemia) may increase your risk of recurring infections—especially in the lungs, sinuses, and gut. This can be due to inherited immune deficiencies, certain medications (like chemotherapy), chronic diseases, or protein loss through the kidneys or digestive tract. People with persistently low levels may require immunoglobulin replacement therapy.

High IgG levels can occur for several reasons:

• Chronic infections: such as hepatitis, mononucleosis, or tuberculosis
• Autoimmune diseases: where IgG may mistakenly attack the body’s own tissues
• Chronic inflammation or certain cancers, like multiple myeloma

If levels are high, further testing can help determine whether it’s part of a normal immune response or a sign of an underlying condition that needs treatment.