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The Test Sample
What is being tested?
Cytomegalovirus (CMV) is a common virus that occurs widely throughout the population but rarely causes symptoms. In the United States, as many as 50-85% of adults have been infected with CMV. Most people are infected as children or as young adults and do not experience any significant symptoms or health problems.
CMV testing involves either a measurement of CMV antibodies, immune proteins produced in response to CMV exposure, or the detection of the virus itself. The virus can be identified during an active infection by culturing CMV or by detecting the virus's genetic material (its DNA) in a fluid or tissue sample.
CMV is found in many body fluids during an active infection, including saliva, urine, blood, breast milk, semen, vaginal secretions, and cerebrospinal fluid. It is easily transmitted to others through close physical contact or by contact with infected objects, such as diapers or toys. After the initial "primary" infection has resolved, CMV becomes dormant or latent, like other members of the herpes family. Cytomegalovirus remains in a person for the rest of the person's life without causing any symptoms unless the person's immune system is significantly weakened. If this happens, the virus can reactivate.
CMV can cause notable health problems in three situations:
- In young adults, primary CMV infection may cause a flu-like or mononucleosis-type illness. This condition, which causes symptoms such as extreme fatigue, fever, chills, body aches and/or headaches, usually resolves within a few weeks.
- In infants, primary CMV infection may cause serious physical and developmental problems. This occurs when a woman is infected for the first time (primary infection) during pregnancy and then passes the infection to her developing baby across the placenta. 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.
- In those with weakened immune systems, CMV could cause serious illness and death. This includes those with HIV/AIDS, those who have had organ or bone marrow transplants, and those undergoing chemotherapy treatment for cancer. People with compromised immune systems who become infected for the first time (primary infection) might experience the most severe symptoms and their CMV infection may remain active. Those who have been exposed to CMV previously may reactivate their infection. This could affect their 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), and brain (causing encephalitis). There can also be spleen and liver involvement, and those who have had organ or bone marrow transplants may experience some degree of rejection. Active CMV also further depresses the immune system, allowing other secondary infections such as fungal infections, to occur.
How is the sample collected for testing?
The sample required depends on the type of testing. Antibody testing requires a blood sample, obtained by inserting a needle into a vein in the arm. Viral detection may be done on a variety of samples, including urine, blood, or sputum. Some samples may require a special procedure to collect, such as amniotic fluid, duodenal fluid, cerebrospinal fluid, or body tissue (biopsy).
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.