Immunoglobulin G (IgG) is the main antibody in the blood, accounting for 75-80% of the total number of antibodies in the body. With its Y-shaped structure, IgG is efficient in binding to various antigens, playing a key role in defense against infection. It provides long-lasting immunity that remembers previous infections and accelerates response upon re-exposure to a pathogen. IgG performs functions such as neutralizing toxins. Measuring IgG levels in the blood is an important diagnostic tool for assessing immune system function and diagnosing a variety of conditions, including immunodeficiencies and autoimmune diseases. Immunoglobulin G also provides passive immunity to newborns by crossing the placenta from the pregnant woman.