Test for measles-specific IgM antibody
This test looks for an antibody called measles-specific IgM in your blood. If you have been exposed to the rubeola virus, your body may have made this antibody. The rubeola virus causes measles, an extremely contagious disease. It is spread through the air in droplets after people cough or sneeze.
Thirty percent of people who catch the measles have complications. These include pneumonia, diarrhea, and ear infections that may cause permanent hearing loss. In rare cases, children may get encephalitis. This is a brain infection that can lead to intellectual disability and deafness.
Measles is much less common than in the past because so many children in the U.S. are now vaccinated against the disease. Most cases in the U.S. are among people who have brought the disease from other countries and spread it to others who are not vaccinated.
You may need this test if you have been exposed to measles and haven't been vaccinated against the disease. If you are infected with the measles virus, you may not develop symptoms for 2 weeks.
You may also need this test if you have measles symptoms. These include:
Rash that starts at the hairline and spreads down the face
Fever that slowly climbs to 103°F (39.4°C) or higher
Red, watery eyes (conjunctivitis)
Your healthcare provider may also order tests for mumps or German measles (rubella).
Test results may vary depending on your age, gender, health history, and other things. Your test results may be different depending on the lab used. They may not mean you have a problem. Ask your healthcare provider what your test results mean for you.
Normal results are negative, meaning you don't have the measles-specific IgM antibody in your blood. A positive result means the antibodies have been found and it's likely you have a measles infection.
Levels of measles-specific IgM antibody in your blood will rise shortly after the rash becomes visible. It may be necessary to repeat the test several days after the rash begins. This should be done in case at the time of the first test the antibodies were not high enough to find in the blood.
The test is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand.
Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be sore.
Timing is important for this test. Your body may not create much IgM antibody at the beginning of the infection, which would give a false-negative result. You may need to have the test again after the rash has been visible for several days. If you've recently been vaccinated against the measles, your IgM antibody level might be higher, giving a false-positive.
You don't need to prepare for this test. Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.