Rubella

The rubella test is used to:

• confirm the presence of adequate protection against the rubella virus
• detect a recent or past infection
• identify those who have never been exposed to the virus and those who have not been vaccinated
• verify that all pregnant women and those planning to become pregnant have a sufficient amount (titer) of rubella antibodies to protect them from infection

Both the IgM and IgG antibody tests may be ordered on a person, pregnant or not, who has symptoms that the doctor suspects are due to a rubella infection. They may also be ordered on a newborn that is suspected to have become infected during pregnancy or that presents with congenital birth defects that the doctor suspects may be due to a rubella infection.

The IgG rubella test is ordered when you are pregnant, planning on becoming pregnant, or whenever a check of immunity against rubella is required. IgM and IgG rubella tests are ordered when a pregnant woman has a fever and rash and/or other symptoms that may indicate a rubella infection. Since many conditions can cause similar symptoms, the doctor will need to order the tests in order to confirm the diagnosis.

IgM and IgG tests may be ordered on a newborn when the mother was diagnosed with a rubella infection during pregnancy and/or when a newborn is born with birth defects (hearing loss, cardiovascular abnormalities, cataracts, central nervous system disease) that could be due to CRS.

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 detectible (when initially absent) and to determine whether the levels are rising or falling over time.

This test may be required of a health care worker or a person starting college and is still ordered on women in some states as part of the blood testing required to obtain a marriage license.

In an adult or child, the absence of IgG rubella antibodies means that the person likely has not been exposed to the rubella virus or been 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 should be immune to the rubella virus. The presence of IgG antibodies, but not IgM antibodies, in a newborn means that the mother’s IgG antibodies have passed to the baby in utero and these antibodies may protect the infant from rubella infection during the initial six months of life. The presence of IgM antibodies in a newborn indicates that the baby was infected during pregnancy (because the mother’s IgM antibodies do not pass to the baby through the umbilical cord). The presence of IgM antibodies, with or without IgG antibodies, in a child or adult indicates a recent infection with the rubella virus.

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, the doctor may order an IgG test to establish a baseline level of antibody and may repeat the IgG test again in 2-3 weeks to look for a significant increase in the amount (titer) present, indicating a recent rubella infection.

It is possible to test for the genetic material (RNA) of the virus directly in a sample or culture a body fluid sample, such as a throat swab, for the rubella virus. The rubella virus takes at least a week or more to be detected in culture, and special molecular assays or specifically prepared antibodies must be used to determine if the virus is present. This may occasionally be done to help a doctor diagnose rubella infection in a newborn. Because this procedure is complex and expensive, most diagnostic laboratories refer this testing to a reference lab such as the Centers for Disease Control and Prevention (CDC). The number of cases of rubella and congenital rubella is monitored by the CDC to track the effectiveness of the rubella vaccine and to detect any outbreaks of the disease.