Serum or plasma immunoglobulin G (IgG) concentration

What Does This Test Measure?

IgG is a type of protein (antibody) produced by your immune system to help fight infections. This test checks the concentration of IgG in your serum or plasma, which can vary depending on your health and immune response. Levels may be lower in people with weakened immune systems or higher in those with certain immune-related conditions.

Why Might You Need This Test?

Your healthcare provider may order this test to evaluate your immune function, diagnose conditions like immunodeficiency, or monitor treatment for diseases affecting antibodies. It can also be used in newborns to check for maternal antibody transfer or in people with chronic illnesses.

Preparation and Sample Collection

No special preparation is usually needed for this test. A blood sample is drawn from a vein, typically in your arm, and sent to a lab for analysis. If you’re taking certain medications or have a condition that affects blood clotting, let your provider know before the test.

What Are Possible Results?

Results are reported as a mass concentration (e.g., grams per liter). While reference ranges can vary by lab, lower than expected IgG levels may indicate immune deficiencies, while higher levels could be seen in chronic infections or autoimmune diseases. Your provider will interpret results in the context of your overall health.