Immunoglobulin G (IgG) in Serum or Plasma

What Does IgG 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 long-term immunity by neutralizing toxins and pathogens. This test helps doctors evaluate your immune response and identify potential deficiencies or overproduction.

Why Might You Need This Test?

Doctors may order an IgG test to diagnose or monitor conditions like immunodeficiency (such as Common Variable Immunodeficiency), autoimmune diseases, infections (e.g., HIV, hepatitis), or to check immune recovery after treatment. It may also be used in newborns to assess maternal antibody transfer or in research settings for antibody profiling.

Sample Collection and Preparation

For this test, a blood sample is drawn from a vein in your arm. The blood is processed to separate serum (the liquid part after clotting) or plasma (the liquid part before clotting). The sample is then sent to a lab for analysis. Avoid eating or drinking for 8–12 hours before the test if fasting is required, as specified by your healthcare provider.

What to Expect Before the Test

You may experience mild discomfort or bruising at the injection site, but most people tolerate blood draws well. If you have a fear of needles, let your healthcare provider know so they can take extra precautions. Wear loose clothing to the appointment to make vein access easier.