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 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 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 test| Positive: | More than 10 international units per milliliter (IU/mL) IgG antibodies. This means that you are immune to rubella and cannot get the infection. |
|---|
More than 1.1 IU/mL IgM antibodies. This means you had a recent rubella infection or you have a current infection. The test for IgM antibodies usually is done only when your doctor suspects that you may have a current rubella infection. |
| Negative: | 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. |
|---|
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
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Saunders.
- Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Credits
| By | Healthwise Staff |
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| Primary Medical Reviewer | John Pope, MD - Pediatrics |
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| Primary Medical Reviewer | Adam Husney, MD, MD - Family Medicine |
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| Specialist Medical Reviewer | Susan C. Kim, MD - Pediatrics |
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| Last Revised | February 1, 2011 |
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