Immunoglobulin G (IgG) mass concentration in serum

What Is IgG and Why Is It Measured?

IgG, or Immunoglobulin G, is the most common type of antibody in your blood. Antibodies are proteins that help your immune system recognize and fight off bacteria and viruses. IgG is particularly important because it can cross the placenta to provide passive immunity to your baby during pregnancy. Your body produces IgG in response to infections and vaccines, helping you remember how to fight specific pathogens in the future. Levels of IgG can vary depending on your health, immune status, and exposure to infections.

When Might You Need This Test?

Doctors may order an IgG test to evaluate your immune system function, diagnose or monitor conditions like immunodeficiency, check for infections, or assess response to treatments such as vaccines or medications. It can also be used in newborns to measure maternal antibodies transferred during pregnancy.

How Is the Test Performed?

A blood sample is taken from a vein, usually in your arm. The blood is then sent to a lab where it is processed to separate the serum (the liquid part without blood cells). The IgG level is measured using a specialized immunoassay technique that detects the antibody concentration.

What Does a Low or High IgG Level Mean?

Low IgG levels may indicate an immune deficiency, where your body struggles to produce enough antibodies to fight infections. This can be congenital (present from birth) or acquired due to certain medical conditions or treatments. High IgG levels might suggest an overactive immune response, chronic infections, or certain autoimmune conditions, though this is less common.