A high IgG level can be an indicator of having a long-term infection such as HIV, states WebMD. Multiple sclerosis, long-term hepatitis and multiple myeloma are also health conditions that cause elevated IgG levels.
IgG antibodies are important for fighting many types of viral, fungal and bacterial infections and cancer, reports HealthLinkBC. In multiple myeloma, only one type of IgG antibody is produced by tumor cells. Hepatitis, multiple sclerosis and HIV cause an increase in several types of IgG antibodies, explains WebMD.
Antibodies attach to foreign substances so they can be destroyed by the immune system, reports HealthLinkBC. All bodily fluids contain IgG antibodies. They are the smallest, most common type of antibodies in the body. IgG antibodies protect the fetus during pregnancy, as they are the only type of antibody that can cross the placenta, states WebMD.