What is Cytomegalovirus (CMV) Tests?
Also Known As:
CMV Blood Test CMV IgG and IgM
Cytomegalovirus Antibody (IgG and IgM) PCR Culture
Cytomegalovirus (CMV) is a common virus that usually causes no symptoms or only mild illness. CMV testing detects antibodies in the blood that the body produces in response to the infection or detects CMV directly.
In the United States, as many as 60% of people have been exposed to CMV at some point in their life. Almost 1 out of every 3 children have been exposed to CMV by age 5 and more than half of adults are exposed to CMV by age 40.
Most people are infected as children or as young adults, but many don’t know it because CMV usually does not cause noticeable symptoms or only mild illness in otherwise healthy people. Individuals with mild illness may have non-specific signs and symptoms, such as sore throat, fever, tiredness, and swollen glands. In otherwise healthy adults, CMV infection may sometimes cause a flu-like illness or signs and symptoms similar to mononucleosis (mono), such as extreme fatigue, fever, chills, body aches, and/or headaches that usually resolve within a few weeks.
CMV is found in many body fluids during an active infection, including saliva, urine, blood, breast milk, semen, vaginal fluid, and cerebrospinal fluid. CMV easily spreads from person to person through close contact with someone who is infected or by contact with contaminated body fluids or objects, such as diapers or toys.
Once you are infected, CMV remains in your body for the rest of your life without causing symptoms. After your initial “primary” infection resolves, CMV becomes dormant or latent, like other members of the herpes family. However, if your immune system is significantly weakened, the virus can become active again (reactivate) and cause illness.
CMV can cause notable health problems in these situations:
- A pregnant woman who is infected for the first time (primary infection) during pregnancy can pass the infection to her developing baby across the placenta. This can cause serious physical and developmental problems in the baby. Most newborns (about 90%) who are infected appear healthy at birth but may develop hearing or vision problems, pneumonia, seizures, and/or delayed mental development a few months later. A few babies may be stillborn, while others may have symptoms at birth such as jaundice, anemia, an enlarged spleen or liver, and a small head.
- CMV can cause serious illness and death in people with weakened immune systems, such as those with HIV/AIDS, solid organ or bone marrow transplant recipients, and cancer patients receiving chemotherapy. These individuals might experience the most severe symptoms and their CMV infection may remain active. CMV may reactivate in those who were previously exposed. The infection could affect the:
- Eyes, causing inflammation of the retina, which can lead to blindness
- Digestive tract, causing bloody diarrhea and abdominal pain
- Lungs, causing pneumonia with a non-productive cough and shortness of breath
- Brain, causing encephalitis
- Spleen and liver
- Organ or bone marrow transplants, causing some degree of rejection
Active CMV also further depresses the immune system, allowing other secondary infections such as fungal infections, to occur.
How is it used?
Cytomegalovirus (CMV) testing is not used to test everyone for a CMV infection. It may be used help diagnose an active, reactivated, or past CMV infection in certain cases, such as:
- Some pregnant women or immune-compromised people with signs and symptoms
- People who may receive an organ or bone marrow transplant
- Newborns with certain birth (congenital) abnormalities
A few different methods of testing may be used depending on the purpose for testing:
Antibody testing (serology)
This type of test detects antibodies in the blood that are produced in response to a CMV infection. It can be used to diagnose a current or past infection by detecting and measuring two classes of CMV antibodies:
- IgM antibodies are produced by the body first in response to a CMV infection. They can be detected in the blood within a week or two after the initial exposure. IgM levels (titers) rise for a short time, then decline and usually fall below detectable levels after a few months. IgM antibody levels rise again when latent CMV is reactivated.
- IgG antibodies are produced several weeks after the initial CMV infection. IgG levels rise during the active infection, then stabilize as the CMV infection resolves and the virus becomes inactive. Once exposed to CMV, you will have some measurable amount of CMV IgG antibody in your blood for the rest of your life, which provides protection from getting another primary infection (immunity).
Healthcare practitioners compare the absence or presence of IgG and IgM antibodies in the same sample or the amount of antibody present (titer) in samples collected one to three months apart (acute and convalescent samples) to distinguish between active and latent CMV.
Direct detection of CMV
Molecular methods such as polymerase chain reaction (PCR) are used to diagnose congenital infections in newborns and may be used to detect and/or confirm active infections in others. These methods may be used to detect the genetic material (DNA) of CMV (qualitative testing) and/or measure the amount of viral DNA in a sample (quantitative, also called viral load). Molecular methods are more sensitive than culture, and positive and negative results are available in a short period of time.
Immune-compromised people with active CMV may be monitored using a variety of CMV tests. Often, healthcare practitioners monitor the amount of virus present (viral load) to determine a person’s response to antiviral therapy.
Viral cultures are not routinely available but may sometimes be used to detect CMV.