Measles IgG antibodies test is used for the diagnosis of measles or mumps infection. Measles is caused by a virus and spreads from person to person threw saliva and airborne droplets. The doctor may suggest this test if there are any symptoms of measles like fever, cough, runny nose, red, watery eyes, white spots inside the mouth (Koplik spots), and skin rash or if a person comes in contact with someone infected with measles. The presence of IgG antibodies indicates prior exposure to the measles virus through infection or immunization.