Mononucleosis spot test

Definition

The mononucleosis spot test looks for two antibodies in the blood that indicate infection with the Epstein-Barr virus (EBV).

Alternative Names

Monospot test; Heterophile antibody test; Heterophile agglutination test; Paul-Bunnell test; Forssman antibody test

Why the Test is Performed

Sometimes, when the body reacts to an infection, antibodies are made that have nothing to do with the germ. These are called heterophil antibodies.

This test looks for such antibodies. It is used to diagnosis infectious mononucleosis, a disease caused by the Epstein-Barr virus (EBV). About 1 week after the onset of the disease, many patients develop heterophile antibodies. The antibodies peak at weeks 2 - 5 and may persist for several months to 1 year. However, a small number of persons with mononucleosis may never develop such antibodies.

How the Test is Performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How to Prepare for the Test

No special preparation is necessary.

How the Test Will Feel

When the needle is inserted to draw blood, you may feel moderate pain, or only a prick or stinging sensation. You may feel throbbing at the venipuncture site for a few minutes after the blood draw.

Risks

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.

Other risks associated with having blood drawn are slight but may include:

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

Considerations

Monospot tests are usually positive in approximately 85% of patients with infectious mononucleosis. Positive test results will not occur until 1 - 2 weeks into the illness.

Normal Results

No heterophil antibodies are detected.

What Abnormal Results Mean

A positive test means heterophil antibodies are present. These are usually a sign of infectious mononucleosis.

On rare occasions, false-positive results may be occur in persons with:

• Leukemia or lymphoma
• Rubella
• Hepatitis
• Systemic lupus erythematosus (SLE)