Rubella Test

Test Overview

A rubella blood test detects antibodies that are made by the immune system to help kill the rubella virus. These antibodies remain in the bloodstream for years. The presence of certain antibodies indicates a recent infection, a past infection, or that you have been vaccinated against the disease.

• The presence of IgM antibodies means you have a current or recent rubella infection.
• The presence of IgG antibodies means you have immunity against the infection. This immunity could have been received either through vaccination for rubella or a past rubella infection.

Rubella (also called German measles or 3-day measles) usually does not cause long-term problems. But a woman infected with the rubella virus during pregnancy can transmit the disease to her baby (fetus). And serious birth defects called congenital rubella syndrome (CRS) could develop during the first trimester. Birth defects of CRS include cataracts and other eye problems, hearing impairment, and heart disease. Miscarriage and stillbirth are also possible consequences for pregnant women. The vaccination to prevent rubella protects against these complications.

A rubella test is usually done for a woman who is or wants to become pregnant to determine whether she is at risk for rubella. Several laboratory methods can be used to detect rubella antibodies in the blood. The most commonly used method is the enzyme-linked immunosorbent assay (ELISA, EIA).

Why It Is Done

A test for rubella is done to find out if:

• A woman who is or wants to become pregnant is immune to rubella.
• A recent infection was caused by the rubella virus. The presence of IgM antibodies means a current or recent infection.
• A person has been vaccinated against rubella. The presence of IgG antibodies indicates immunity received through either vaccination or a past infection.
• Health professionals who are in contact with pregnant women have had rubella. A health professional who has not had rubella may need to be vaccinated to prevent the risk of spreading rubella to a pregnant woman.

Some babies born with birth defects may be tested for congenital rubella.

How To Prepare

No special preparation is required before having this test.

How It Is Done

The health professional taking a sample of your blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure on the site and then put on a bandage.

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

Blood test

There is very little chance of a problem from having a blood sample taken from a vein.

• You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.

Results

A rubella blood test detects antibodies that are made by the immune system to help kill the rubella virus. The results of a rubella test are given in titers. Titers measure how much the blood sample can be diluted before the antibodies can no longer be detected.

What Affects the Test

There are no factors that would interfere with the test or the accuracy of the results.

What To Think About

• If a woman who wants to become pregnant has not had rubella, she can receive a shot (vaccination) to help protect her against getting the disease. But she must wait 1 month after she gets the shot before becoming pregnant to fully protect her baby.
• A woman should not get a rubella shot while pregnant, and she should avoid people who have or may have rubella.
• A rubella virus culture is not often done because it is a more difficult test.
• Exposure to rubella in the third trimester may not be as serious since the baby (fetus) is fully developed. But these babies can have the infection and be contagious.
• If congenital rubella is suspected, both the mother and her baby need blood tests.

References

Other Works Consulted

• Centers for Disease Control and Prevention (2001). Control and prevention of rubella: Evaluation and management of suspected outbreaks, rubella in pregnant women, and surveillance for congenital rubella syndrome. MMWR, 50(RR-12): 1-23.

• Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

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