Diagnosis
There are several CMV tests that measure different things:
How can I know if I've ever been infected with CMV?
A blood test for IgG antibodies (special immune system proteins) is how your doctor can determine whether you've ever been infected with CMV. By itself, this test won't show whether you were infected during your pregnancy, nor will it tell you whether your fetus has been infected with CMV. If you test negative before your pregnancy, you should take special care to prevent CMV infection while you are pregnant.
How can I know if I've been infected with CMV during my pregnancy?
New CMV infections can be found by doing testing for a type of antibodies ("IgG" antibodies) on blood samples taken at different times. If the first sample is negative and the second sample is positive, then you became infected with CMV sometime between the two samples. A new method, called IgG avidity testing, needs only one blood sample to show whether you have a recent CMV infection. However, this test is currently not commercially available in the U.S. In the past, a test for IgM antibodies (another immune system protein) has been done to try to detect recent infections. Because this test is often positive when there is no new CMV infection, it should not be used without the other tests.
How can I know if my fetus has been infected with CMV?
For these reasons, and because there are no safe and effective CMV drugs for pregnant women, we do not recommend routine screening to see if a fetus is infected with CMV. Blood tests are sometimes used to find women who have new CMV infections. These women have a high risk (about
1/3) of passing the virus to their fetus. Tests of amniotic fluid or fetal blood, along with ultrasound readings
of women, often can identify which of these women passed the virus to their fetus. However, these tests are invasive and don't always correctly identify infected fetuses or fetuses who will have health problems.
How can I know if my newborn has congenital (meaning present from birth) CMV?
A newborn has congenital CMV if the virus can be found in their urine, saliva, or blood during the first 3 weeks after birth. Rather than detecting antibodies, tests must identify the virus itself. Congenital CMV cannot be diagnosed if the baby is tested more than 3 weeks after birth, since she/he could have been infected after birth.
Babies infected after birth are not at risk for disabilities. If your baby has congenital CMV, you should have her hearing and vision tested regularly. Most CMV-infected babies grow up with normal health, but if your child has delayed hearing or vision problems, early detection can help his or her development.
Should I
be tested for CMV if I
am planning a pregnancy?
If you are planning to
become pregnant, a CMV
blood test (which tests
for IgG antibodies -
special immune system
proteins) can help you
know how careful you
must be to prevent CMV
infection. If you
test positive, you will
know that there is
little chance that your
baby will be harmed by
CMV. If you test
negative, carefully
follow the
recommendations for
preventing CMV infection
before and during your
pregnancy. Either
way, it is always a good
idea to follow the
prevention guidelines
because they will help
you avoid other
infections as well.
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