Rubella IgG avidity assay is a qualitative test to differentiate between primary and non-primary infection. To exclude primary infection, Rubella IgG reactive samples should be tested for Rubella IgM and Rubella IgG avidity. The IgG avidity test is indicated as an aid in the diagnosis of symptomatic primary infection and to make the differential serological diagnosis between asymptomatic primary infection and reinfection with the rubella virus, especially in pregnant women.