Rubella Ab., IgG 

This test looks for specific antibodies created to combat the rubella virus.  These antibodies have a long lifespan and can remain in the body for years, so measuring the amount of them can determine if rubella has been present recently or in the past, or if the body is vaccinated against it.  This test is often performed on pregnant women to prevent passing on rubella, which can cause various birth defects if left untreated.