The normal adult range for IgG blood level is 700 to 1,500 mg/dL or 7 to 15 grams per liter, states WebMD. High levels of IgG are symptoms of diseases such as IgG multiple myeloma, hepatitis and multiple sclerosis. Long-term infections, including HIV, lead to inflated IgG levels.
IgG is the most common antibody produced by the body's immune system, according to Johns Hopkins Medical, so reduced levels of IgG are also a concern. When people have IgG deficiencies, they are more open to diseases, including bronchitis, pneumonia and ear and sinus infections. In addition, pneumonia and flu vaccines are often not effective for these individuals.