A normal level of IgG antibodies in an adult is between 700 and 1500 milligrams per deciliter, according to WebMD. A high level may indicate a chronic infection or other medical condition, while a low level may indicate diseases such as macroglobulinemia, leukemia or kidney disease.
Chronic infections, such as HIV, may cause elevated IgG antibody levels, according to WebMD. Other medical conditions that can result in elevated IgG levels include multiple myeloma, chronic hepatitis and multiple sclerosis. Rarely, some people have a congenital inability to produce IgG antibodies, and as a result, these people are more prone to develop infections.