Rubella is a viral infection, which occurs once in a lifetime. Rubella is harmful if, and only if, fresh infection occurs during pregnancy (especially early pregnancy). The rubella antibody tests (IgG and IgM) are part of the ToRCH test, and are used to check for protection against the rubella virus as well as to detect a recent or past infection. They can also be used to identify those who have never been exposed to the virus and those who have not been vaccinated.
Since IgM and IgG rubella antibodies take some time to appear after infection, the tests may be repeated in 2 to 3 weeks to see if the antibody levels have become detectable (when may initially be absent) and to determine whether the levels are rising or falling over time.
Occasionally, a patient will have a false positive test for IgM rubella antibodies because the test components cross-react with other proteins in their body. To confirm the IgM result, an IgG test could be done to establish a baseline level of antibody and repeat the IgG test again in 2-3 weeks to look for a significant increase in the titre, indicating a recent rubella infection. IgG antibodies are developed by an individual after a natural infection as well as after vaccination and persist nearly lifelong. The IgG rubella test is ordered on all pregnant women and those planning to become pregnant to verify that they have a sufficient titre of rubella antibodies to protect them from future infection. Absence of IgG rubella antibodies means that the person likely has neither been exposed to the rubella virus nor vaccinated and is not protected against it. The presence of IgG antibodies (but not IgM antibodies) indicates a history of past exposure to the virus or vaccination and indicates that the person tested is immune to the rubella virus.
In a study in Indian women, rubella IgG was detected in nearly 92% of pregnant women and 89% of non-pregnant women of childbearing age. The authors concluded that majority of the Indian women possess protective level of rubella IgG antibodies. However screening to detect non-immune women is necessary to prevent congenital rubella syndrome in affected children in subsequent pregnancies. IgG antibodies against rubella are tested to look for immunity against this virus and their presence is virtually a guarantee that you will not get this infection during your next pregnancy. Presence of IgG antibodies against Rubella virus more than or equal to 10-15 IU/ml indicate prior or current exposure to rubella virus infection. Anyone having an anti-rubella IgG titre more than 20 IU/ml is considered to be immunologically protected. So get your rubella IgG levels done to allay your anxiety. Also IgM rubella index values of 0.80 to 1.20 are considered equivocal, and must be retested. If the result is equivocal again, then repeat testing is advisable from a good lab after 2-3 weeks.