Immunoglobulin G is a type of antibody. In normal serum, about 80% is IgG. Increased serum immunoglobulin concentrations occur due to polyclonal or oligoclonal immunoglobulin proliferation in hepatic disease (hepatitis, liver cirrhosis), connective tissue diseases, acute and chronic infections, as well as in the cord blood of neonates with intrauterine, perinatal infections and polyclonal immunoglobulin production. Monoclonal elevations of IgG characterize multiple myeloma. Decreased immunoglobulin levels are found in patients with congenital deficiencies, primary or secondary immune deficiencies.