Immunoglobulins play a key role in the body’s immune system. They are proteins produced by specific immune cells called plasma cells in response to bacteria, viruses, and other microorganisms as well as exposures to other substances that are recognized by the body as “non-self” harmful antigens. This test measures the amount of immunoglobulins G in the blood. About 70-80% of the immunoglobulins in the blood are IgG. Specific IgG antibodies are produced during an initial infection or other antigen exposure, rising a few weeks after it begins, then decreasing and stabilizing. The body retains a catalog of IgG antibodies that can be rapidly reproduced whenever exposed to the same antigen. IgG antibodies form the basis of long-term protection against microorganisms. In those with a normal immune system, sufficient IgG is produced to prevent re-infection. Sample: Blood (serum) Reference: Between 700 mg/dl and 1600 mg/dl Frequency: Twice a week