Rubella test

A blood test can determine if you have had a recent or past infection, or if you have never been exposed to the rubella virus. People with recent infection will have a positive IgM antibody and those with a past infection (and those who have been vaccinated for rubella) will have a positive IgG antibody, while neither antibody will be present if there has been no contact with the virus. A blood test for both antibody types will help the doctor predict if you are protected from infection or if you are at risk.

If you are pregnant and have exposure to a person with a rubella-like rash and flu-like symptoms or you develop a rash and symptoms, your doctor should request a laboratory test to help diagnose possible rubella infection. It is a particularly important to test for rubella in early pregnancy as infection during the first 16 weeks of pregnancy presents major risks for the unborn baby. Antibody testing is strongly recommended for women planning a pregnancy so those who are not immune to the virus can be vaccinated before they conceive. Antibody testing is often used in infants born with abnormalities, such as deafness, mental retardation, heart defects, and cataracts that may have resulted from a rubella infection acquired before their birth.

In an adult or child, the absence of IgG antibodies to rubella means the person is not immune. Absence of IgM antibodies and presence of IgG antibodies indicates a history of past exposure to the virus or vaccination. Presence of IgM antibodies with or without IgG antibodies usually represents recent infection. In an infant the presence of IgM antibodies means the baby was infected during the pregnancy. Occasionally, low levels of IgM antibodies represent a false positive result. A positive IgM result, particularly in pregnancy, needs to be interpreted with care.

If only a low level of antibodies are detected then the test may be inconclusive, and immunisation with the rubella vaccine may be recommended as a precaution.