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Cytomegalovirus (Blood)

Does this test have other names?

CMV (serum), cytomegalovirus serologic test, cytomegalovirus antibody, IgG, IgM

What is this test?

This test looks for antibodies to cytomegalovirus (CMV), a virus in the herpes family, in your blood.

CMV is so widespread that most people in the U.S. have been infected by the time they reach age 40, although many don't realize it. You can pick up the virus by handling or exchanging bodily fluids, including kissing or having sex. The virus usually causes only a mild illness, but it can do serious harm to unborn children, people with HIV/AIDS, or others with a weak immune system.

Antibodies are germ-fighting molecules that your immune system makes in response to infection. If you have CMV-specific antibodies in your blood, you may have a CMV infection.

Like other herpes family viruses, cytomegalovirus hides in the body after the first infection and can flare up again. Later infections tend to be milder. In fact, in adults with a healthy immune system, the first infection may not have any symptoms.

Why do I need this test?

You may have this test if you have unexplained symptoms that resemble the flu. If you've been infected with the virus, you may have these signs and symptoms:

  • Prolonged high fever

  • Fatigue

  • Muscle and joint pain

  • Headache

  • Sore throat

  • Swollen lymph nodes

  • Swollen liver and spleen

You may also have this test if you are pregnant, have HIV or are a transplant donor or recipient. If you have a current infection, your doctor can give you certain medications to reduce the danger of congenital CMV in infants or of active illness in people with a weakened immune system.

Only a lab test can confirm that you have CMV.

What other tests might I have along with this test?

Your doctor may also order other tests for CMV antibodies. These include tests of  your cerebrospinal fluid (CSF) and urine. Your doctor may also order tests to look for CMV antigens that CMV antibodies are meant to fight. A CMV antigen test may be called a CMV antigen assay or a CMV Ag test. (Ag stands for antigenemia, meaning antigen-in-blood.)

Your doctor may also order a test called polymerase chain reaction to hunt for the DNA of CMV in your urine, saliva, blood, CSF, or biopsy tissue. He or she may also order a viral culture test from any of these sample types.

Your doctor may also order:

  • Complete blood count, or CBC

  • Mononucleosis or Epstein-Barr virus test

He or she may also test for pneumonia, hepatitis, and gastrointestinal problems.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results are given in amounts of two kinds of antibodies: immunoglobulin M (IgM) and immunoglobulin G (IgG).

If your IgM and IgG levels are high, it may mean you have CMV. Your doctor will likely give you the test again in two weeks to confirm the infection. If your IgG levels rise fourfold between the first and second test, that will confirm an active infection. The fact that your IgG level increases is more important than the amount of IgG found. The increase shows that your immune system is busy fighting an infection and that the antibodies are not just left over from an earlier fight.

If your results are higher, it may also mean that you have a connective tissue autoimmune disease, such as rheumatoid arthritis or systemic lupus erythematosus.

If your immune system is weakened, you may have lower results even with an active infection.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Other factors aren't likely to affect your results.

How do I get ready for this test?

You don't need to prepare for this test. But be sure your doctor knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use.