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
In general, there's nothing you have to do before this test, unless your doctor tells you to.
How It Is Done
A health professional uses a needle to take a blood sample, usually from the arm.
How It Feels
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
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.
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.
A test for rubella IgM antibodies is done only if the doctor suspects that you have a current rubella infection.