Approximately 80% of serum immunoglobulin is IgG whose main functions are defense against microorganisms, direct neutralization of toxins and induction of complement fixation. IgG is the only immunoglobulin that can cross the placental barrier and provide passive immune protection to the fetus and newborn. Near adult levels are reached by 18 months. Polyclonal IgG increase is seen in SLE, Chronic liver diseases, Infectious diseases and Cystic fibrosis. Monoclonal IgG increase is seen in IgG Myelomas. Decreased synthesis of IgG is found in Congenital and Acquired Immunodeficiency diseases and selective IgG subclass deficiency. Decreased IgG levels are seen in Protein losing enteropathies, Nephrotic syndrome and skin burns.