CMV

Other names: Cytomegalovirus

The CMV test is used to test for the presence of the CMV virus (cytomegalovirus). CMV is a very common virus and it is estimated that between 50% and 85% of adults in the UK have been affected by the virus. The virus is most common amongst children and it may not contribute to any symptoms; the virus stays in the body for the rest of a person’s life but it may not cause any symptoms and will generally only contribute to an infection if the individual’s immune system becomes compromised.

The CMV virus can be very dangerous in foetuses and infants; the foetus can become infected if the mother is infected for the first time during pregnancy. 90 percent of babies who are infected experience no problems initially but may go on to develop problems with development; others may experience symptoms, including jaundice and anaemia at birth. In rare cases, the baby may be stillborn.

The CMV virus can also be life-threatening for those with compromised immune systems, such as patients with HIV.

Why is the test used?

The test can be used for two main purposes: to detect the virus and to check for antibodies. The presence of antibodies suggests that the patient has been infected with CMV in the past. Antibody testing is also used to test for immunity in pregnant women and patients who are about to undergo transplant surgery.

The test is usually ordered when patients who have a compromised immune system, pregnant women or young children have symptoms of an active CMV infection; symptoms include nausea, fatigue, a high temperature and inflamed lymph nodes. The test will also be ordered for patients who have a compromised immune system when they have symptoms including swelling of the liver, lungs, eyes or gastrointestinal tract.

The test may also be ordered if a newborn baby has symptoms of a CMV infection, including anaemia, jaundice, a small head and an enlarged spleen.

How is the test done?

If the test is being carried out to test for antibodies, a blood sample will be taken from a vein in the arm. Once the blood has been collected, it will be bottled, labelled and sent away to the laboratory for analysis.

If the test is being carried out to detect the presence of the virus, different samples, including sputum and urine samples, as well as a blood sample, may be collected and analysed.

What do the test results mean?

It is often difficult to determine whether a patient has an active or a latent CMV infection because the virus stays in the body for the rest of a person’s life. Patients with a compromised immune system and newborn babies may have a poor response to an infection because their immune systems are not strong; this may mean that their antibody levels are lower than expected.

If the sample shows that CMV is present in the bloodstream and the patient has symptoms associated with CMV infection, it is very likely that the patient has an active infection. If levels are low and the patient does not have any symptoms, this may indicate that the patient has had an infection recently but has recovered; low levels may also mean that the patient has a non-symptomatic infection.

If the test has been used to detect antibodies and the results show that both CMV IgG and IgM are present and the patient has symptoms, it is highly likely that the patient has an infection; it may be the first time they have had a CMV infection or the CMV may have been reactivated. If neither CMV antibody is detected, it is likely that the patient has a different type of infection. If only IgM is detected, the individual may have been infected by the virus very recently; if a newborn baby has IgM antibodies, they have a congenital CMV infection.

Specific Blood Tests

Blood Test Guide

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