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What is a Cytomegalovirus (CMV) test?
Cytomegalovirus or CMV is a type of herpes virus, that causes mild to almost no symptoms in most cases; rarely, it produces severe symptoms and causes mononucleosis.

A CMV test is a blood test that evaluates antibodies against CMV. Upon infection, CMV harbours in the body and remains latent throughout life without causing any symptoms. However, if the immune system of such individuals weakens, it results in reactivation of the virus causing illness. In addition, CMV is also known to weaken the immune system, increasing susceptibility to other infections, particularly fungal.

  1. Why is a CMV test performed?
  2. How do you prepare for a CMV test?
  3. How is a CMV test performed?
  4. What do CMV test results indicate?

A CMV test is performed in pregnant women or immunocompromised patients who suffer from flu-like conditions or the following symptoms:

If a pregnant woman transmits CMV to the foetus, it can result in miscarriage, stillbirth or death of the newborn.A CMV test is performed in an infant or newborn if he/she has:

  • Jaundice (yellowing of the skin or eyes)
  • Low platelet count
  • Small head size
  • Seizures
  • Enlarged spleen or liver
  • Hearing and vision difficulties
  • Pneumonia
  • Signs of delayed mental development

This test is also performed when a person is undergoing an organ or bone marrow transplant to check if he/she is exposed to CMV in the past. CMV is tested at regular intervals in people who have received a transplant or are undergoing antiviral therapy (to monitor the effectiveness of the therapy).

No special preparations are needed for this test.

It is a simple procedure that takes less than five minutes. An experienced laboratory specialist will withdraw a blood sample from a vein in your arm by inserting a small needle. A small quantity of blood will be collected into a sterile vial or a test tube. You may feel a momentary pricking pain when the needle goes in the vein.
Also, there is a minimal risk of pain, light-headedness and bruising at the site of injection associated with the test. However, at most times, these symptoms disappear quickly. Rarely, an infection may occur at the site of withdrawal of blood.

Apart from the blood test, the virus can be checked for (instead of antibodies) in the urine, sputum, cerebrospinal fluid (CSF), amniotic fluid, saliva or body tissues of a newborn.

Normal results: Absence of CMV antigen or antibodies (IgM or IgG) against CMV indicate normal results, which means that the individual has not been exposed to CMV. Negative IgM or negative IgG indicate no current or prior CMV infection.

Abnormal results: Positive IgM and negative IgG indicate active primary infection or repeat exposure to CMV or latent CMV reactivation. Positive IgM and very high levels of IgG (four-fold increase in the IgG levels) indicate primary CMV infection or reactivation of the latent infection. A negative IgM but a positive IgG indicate past exposure to CMV or latent CMV infection.
Negative IgM and/or negative IgG with symptoms of an infection may signify infection due to other microorganisms or due to a very poor immune status, which is not allowing adequate production of antibodies against CMV.

A positive CMV DNA test indicates the presence of an active infection. A high level of viral DNA indicates a more severe form of CMV infection, whereas low levels of viral DNA signify mild or non-active infection. Negative CMV DNA indicates no infection.

While evaluating the response to antiviral therapies, viral DNA level (or viral load) is measured sequentially for better evaluation. Low levels or dipping levels of viral DNA indicate a positive response to the therapy.

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.

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  1. Center for Disease Control and Prevention [internet], Atlanta (GA): US Department of Health and Human Services; Cytomegalovirus (CMV) and Congenital CMV Infection
  2. Child Care Aware. [Internet] U.S. The Danger of Spreading CMV: How We Can Protect Our Children
  3. Lab tests Online. [Internet] American Association of Clinical Chemistry, U.S. Cytomegalovirus (CMV) Tests
  4. University of Rochester Medical Center. [Internet]. Rochester (NY): University of Rochester Medical Center; Cytomegalovirus (Blood)
  5. National Cytomegalovirus Foundation. [Internet] Tampa, Florida, U.S. CMV transmission