Mononucleosis spot test detects the presence of heterophile antibodies. Heterophile antibodies are antibodies that non-specifically react against different proteins and are useful in the diagnosis of infectious mononucleosis.

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell 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.

In infants or young children: 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. A bandage may be applied to the puncture site if there is any bleeding.

No special preparation is necessary.

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.

The mononucleosis test is done to screen for the presence of 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. A small proportion of patients with mononucleosis may never develop heterophile antibodies.

Normal results are negative, which is indicated by a titer ratio of less than 1:40.

A positive test (titer greater than 1:40) usually indicates infectious mononucleosis. On rare occasions, false-positive tests may be seen with the following:

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

• 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

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.