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, including pneumonia, diarrhea, and ear infections that may cause permanent hearing loss. In rare cases, children may develop encephalitis. This is a brain infection that can cause intellectual disability and deafness.
Because so many children in the U.S. are now vaccinated against the measles, the disease is much less common than it was in the past. Most cases in the U.S. are among people who have brought the disease from other countries and spread it to others who are unvaccinated.
You may need this test if you have been exposed to measles and have not previously been vaccinated against the disease. If you are infected with the measles virus, you may not develop symptoms for two weeks.
You may also need this test if you have symptoms of measles, including:
Rash that starts at the hairline and spreads down the face
Fever that gradually climbs to 103 degrees or higher
Pinkeye, or conjunctivitis
Your doctor may also order tests for mumps or German measles, also called rubella.
Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.
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.
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.
The test requires a blood sample, which is drawn through a needle from a vein in your arm.
Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.
You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.