Serum or Plasma Immunoassay for Immunoglobulin G (IgG) Substance Concentration

Why This Test Is Done

Your healthcare provider may order this test to check for immune system health, diagnose conditions like low IgG levels (hypogammaglobulinemia), evaluate immune responses to vaccines or treatments, or monitor immune-related diseases such as lupus, HIV, or certain cancers. It may also be used to assess how well your body is responding to infections or treatments for autoimmune disorders.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if your blood is drawn early in the morning. Avoid strenuous activity or excessive caffeine on the day of the test. If you’re on blood thinners or have a history of bleeding disorders, let your provider know.

How the Test Is Performed

A healthcare professional will collect a blood sample from a vein in your arm using a needle. The blood is then sent to a lab for analysis using an immunoassay method to measure IgG levels. The process typically takes a few minutes, and you may feel a brief pinch or slight discomfort.

What the Results Mean

IgG levels can vary based on age, overall health, and medical conditions. While reference ranges aren’t provided here, your results will be compared to standards appropriate for your age and health status. Low IgG levels may suggest immune deficiencies, while very high levels could indicate chronic infections, certain cancers, or autoimmune diseases. Your provider will interpret the results in the context of your overall health.