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 means a recent infection, a past infection, or that you have been vaccinated against the disease.
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, especially 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 means 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.
Results
A rubella blood test detects antibodies that are made by the immune system to help kill the rubella virus. The test for IgG antibodies is most common and is the test done to see if a woman who is pregnant or planning to get pregnant is immune to rubella.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Rubella blood testfootnote 1
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Positive:
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More than 10 international units per millilitre (IU/mL) IgG antibodies. A positive rubella IgG test result is good—it means that you are immune to rubella and cannot get the infection. This is the most common rubella test done.
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Negative:
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Less than 7 IU/mL IgG antibodies and less than 0.9 IgM antibodies. This means you are not immune to rubella. If you are a woman thinking about getting pregnant, talk with your doctor about getting a rubella vaccine before pregnancy.
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A test for rubella IgM antibodies is done only if the doctor suspects you have a current rubella infection. More than 1.1 IU/mL IgM antibodies means you had a recent rubella infection or you have a current infection.footnote 1
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 she is 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
Citations
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Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
Other Works Consulted
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Credits
Current as of:
May 27, 2020
Author: Healthwise Staff
Medical Review:
John Pope MD - Pediatrics
Anne C. Poinier MD - Internal Medicine
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Kathleen Romito MD - Family Medicine
W. David Colby IV MSc, MD, FRCPC - Infectious Disease
Christine Hahn MD - Epidemiology
