Testing

If a pregnant woman has symptoms of a CMV infection, blood tests can identify special proteins in the blood (antibodies) that are created by the immune system to fight off a CMV infection. The virus can also be detected by culturing or by a polymerase chain reaction (PCR) test from blood, other body fluids, or a tissue biopsy.

For newborns, the diagnosis of congenital CMV is confirmed by isolating and growing the virus from urine, saliva, or tissue that is collected during their first three weeks of life. Urine usually is tested because it contains the highest concentration of the virus, referred to as the "gold standard". A positive viral culture collected beyond the three week period but within the first year of life should be considered a possible congenital CMV infection, but also may be an acquired CMV infection.

Testing Recommendations

CMV Testing Before Pregnancy

Women who are interested in being tested for CMV prior to pregnancy can speak to their doctor and request CMV IgM and IgG antibody labs. If they have been exposed to CMV, it is recommended that women wait until their CMV IgM antibody levels decline to an undetectable level and their CMV IgG avidity index climbs to a high favorable percentage. This would indicate that the primary CMV infection has resolved itself and that there is minimal risk of CMV transmission to a new baby. It may take 6 to 12 months for CMV antibody and avidity tests to be favorable and for a woman to be ready to conceive.

CMV Testing During Pregnancy

The Centers for Disease Control and Prevention (CDC) do not recommend routine maternal screening for CMV infection during pregnancy because there is no test that can definitively rule out primary CMV infection during pregnancy. Occasionally the need for CMV testing arises when abnormalities that may be caused by CMV or other infectious diseases are seen on ultrasound. If a CMV infection is detected during pregnancy, amniocentesis is an option during which a doctor obtains and examines a sample of amniotic fluid to determine whether the baby has congenital CMV.

CMV Testing of Newborns

Congenital CMV is more common that the combined conditions and disorders currently screened for in the United States core newborn screening panel. Unfortunately, newborns are not routinely tested for CMV at birth.

If you find out that you became infected with CMV for the first time during your pregnancy, it is important that they be tested within the first three weeks of birth when a diagnosis of congenital CMV can be made if the virus is found in a newborn's urine, saliva, blood, or other body fluids.

Congenital CMV cannot be accurately diagnosed if the newborn is tested more than 2-3 weeks after birth. After 3 weeks, tests won't be conclusive for congenital CMV because the baby could have contracted the infection through nursing or by exposure to siblings or others who may be shedding the virus.

Pregnancies After CMV

Pregnant women who have already been exposed to CMV prior to pregnancy will have CMV antibodies in their blood and there is a very small chance that a CMV reactivation would infect their unborn child. But those women who have experienced a CMV infection during pregnancy, a fetal loss due to CMV, or a newborn with congenital CMV should discuss these factors with their doctor, who may recommend CMV IgM and IgG antibody labs to be drawn. Most experts recommend that women wait until their CMV IgM antibody levels decline to an undetectable level and their CMV IgG avidity index climbs to a high favorable percentage. This would indicate that the primary infection has resolved itself and that there is minimal risk of CMV transmission to the new baby. It may take 6 to 12 months for CMV antibody and avidity tests to be favorable and for a woman to be ready to conceive.

Testing Options

Antibody Testing

CMV antibodies are special proteins found in blood that are created by the immune system to fight off a CMV infection. Antibody, or serologic tests, are used to diagnose CMV infection by detecting the two types of CMV antibodies, IgM and IgG. By comparing the absence or presence of both IgG and IgM antibodies within the same testing sample, a doctor can distinguish between a primary (active), inactive (latent/dormant), and reactivated or recurrent CMV infection.

The TORCH test is a common antibody test performed on pregnant women and newborns to detect antibodies of four major causes of congenital (before birth) infection. TORCH is an acronym for the antibodies detected by the test: Toxoplasma gondii (toxoplasmosis), rubella (German measles), cytomegalovirus (CMV), and herpes simplex virus (HSV).

IgM Anitbody Testing

The IgM antibodies are present in most people within a week or two after initial CMV exposure and are the first to be produced by the body in response to a CMV infection. IgM antibody production will increase for a short time period then will decline. Eventually, after several months, the level of CMV IgM antibody usually falls below detectible levels. The presence of CMV IgM should not be used by itself to diagnose a primary CMV infection.

CMV IgM is detectable when a person 1) is newly infected with a primary CMV infection, 2) has been infected in the past but recently re-exposed to CMV, 3) is undergoing reactivation of CMV infection that was acquired in the past, or 4) has a false-positive test result.

IgG Antibody Testing

Levels of IgG antibody increase during an active CMV infection, then will stabilize as the CMV infection resolves and the virus becomes inactive, or dormant/latent. When a person has been exposed to CMV, they will have some measurable amount of CMV IgG antibody in their blood for the rest of their life.

A positive test for CMV IgG indicates that a person was infected with CMV at some time during their life, but the IgG test does NOT indicate if that person is actively shedding the virus and cannot determine when a person was infected with CMV.

Avidity Testing

IgG avidity assays (or tests) measure antibody maturity and have been shown to reliably detect recent primary CMV infection. When a person has a primary CMV infection, the body produces low-avidity IgG. After 2-4 months, the body begins to produce high-avidity CMV IgG. Low CMV IgG avidity suggests a primary CMV infection occurred within the past 2-4 months. High CMV IgG avidity suggests that CMV infection occurred at some point in the past. In the United States, CMV IgG avidity tests are not yet widely available commercially.

Viral Testing

Viral culture is the traditional method of virus testing and involves culturing blood, saliva, urine, or a tissue biopsy, inoculating a culture/tube of human cells with the patient’s sample, and incubating the culture in a supportive environment. Positive cultures can often be detected in as little as 1 to 2 days, but negatives must be held for 3 weeks to confirm the absence of CMV (because the virus may be present in very low numbers and/or the CMV strain may be slow-growing).

DNA Testing

CMV DNA testing may be used to detect and measure the amount of the virus’ genetic material (CMV DNA) in a patient’s sample. CMV DNA testing can be qualitative, determining the presence or absence of CMV, or quantitative, measuring the amount of CMV present in the sample.

Polymerase chain reaction (PCR) Testing

Active CMV infections can also be diagnosed by polymerase chain reaction (PCR) tests which can detect CMV from blood, saliva, urine, placenta, throat swab, or tissue biopsy. PCR is considered to be as/more sensitive as urine, and is simple, and cost-effective.

Viral Load Testing

Quantifiable viral tests, or "viral loads", track the amount of CMV present within the sample, referred to as the viral load.