Alternative Names: CMV antibody tests

How the test is performed:

Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

Serology refers to the study of serum (the fluid portion of blood) for its antibody content. An antibody defends the body against bacteria, viruses, fungus, or other foreign bodies (antigens). Certain microbial cells stimulate the body to produce these antibodies during active infection. Antibody production increases during the course of infection.

In the initial stage of an illness, few antibodies may be detected. For this reason, serology tests are often repeated a few weeks after the initial sample. The presence of antibodies can also indicate a prior CMV infection. This is important in CMV, because a latent infection can be reactivated to produce active infection.

In the laboratory, the antibodies react with antigens in specific ways that can be used to confirm the identity of a specific microorganism. There are several serology techniques that can be used depending on the suspected antibodies. Serology techniques include agglutination, precipitation, complement-fixation, fluorescent antibodies, and others.

How to prepare for the test:

There is no special preparation for the test.

How the test will feel:

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed:

The test is performed to detect current active CMV infection, or past CMV infection in people who are at risk for reactivation of infection (such as organ transplant recipients and people with a suppressed immune system). The test may also be performed to detect CMV infection in newborns.

Normal Values:

People who have never been infected with CMV have no detectable antibodies to CMV.

What abnormal results mean:

A specimen with positive antibodies to CMV indicates a current or prior infection with CMV. If the number of antibodies rises over an interval of a few weeks, this may signify the presence of an acute infection.

Chronic CMV infection (where the antibody count stays about the same over time) can become reactivated in a person with a suppressed immune system.

What the risks are:

The risks associated with having blood drawn are:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins

Special considerations:

To detect specific organ system infection with CMV, cultures of the specific organ can be obtained.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.