Mononucleosis Spot Test

Written by Colleen M. Story | Published on July 25, 2012
Medically Reviewed by Brenda B. Spriggs, MD, MPH, FACP


A mononucleosis spot test is a simple blood test used to determine whether or not you are infected with the Epstein-Barr virus, which causes infectious mononucleosis. A doctor may order this test if you have symptoms of mononucleosis, a viral disease that affects certain blood cells and creates flu-like symptoms.

What Is Mononucleosis?

Mononucleosis is a viral infection usually caused by the Epstein-Barr virus (EBV), which is a type of herpes virus and one of the most common human viruses. Also called "mono" and "the kissing disease," the illness is not considered serious or life threatening. This disease typically affects teenagers and young adults in their 20s. The symptoms of infectious mononucleosis can make it difficult to continue with normal daily activities, and may last from several weeks to a couple of months.

Symptoms of mononucleosis include:

  • fever
  • sore throat
  • swollen glands
  • unusual fatigue
  • headaches
  • loss of appetite
  • night sweats
  • swollen spleen (sometimes)

If you have these symptoms for more than a week or so, you may have mono. To confirm the diagnosis, your doctor may perform the mononucleosis spot test.

What Happens During a Mononucleosis Spot Test?

This procedure is most often performed between two and nine weeks after a person is infected and this test helps confirm a diagnosis of the illness. Like most blood tests, it’s performed by a nurse or other healthcare professional who withdraws a blood sample from a vein, usually on the inside of the elbow or the back of the hand. (Sometimes a simple finger-prick test may be used instead.)

The professional wraps an elastic band around your upper arm to make the vein fill with blood, then gently inserts a small needle into the vein, allowing the blood to flow into an attached tube. When the tube contains enough blood, the professional withdraws the needle and covers the small puncture wound with a bandage.

For a finger-prick test, the professional makes a small prick in the tip of your ring finger, then squeezes to collect enough blood in a small tube to perform the test. A bandage is placed over the small wound afterward.

Are There Any Potential Complications Associated With the Test?

Though blood tests are extremely safe, some people may feel light-headed after it’s over. If you experience lightheadedness, tell the nurse, and sit down in the office until it passes. The nurse may also get you a snack and a beverage to help you recover.

Other complications may include soreness at the injection site, particularly if the healthcare professional had a hard time reaching your veins. Obtaining a blood sample can sometimes be difficult if the vein is particularly small or difficult to see. In these cases, you may also have a slight risk of hematoma, which is basically a bruise. This will typically heal on its own after a few days. If you notice any swelling, a warm compress may help.

As with all procedures that create an opening in the skin, there is a rare chance of infection. Your healthcare professional will use an alcohol swab to wipe the place of insertion beforehand, which almost always prevents infections. However, you should watch for any development of swelling or pus, and be sure to keep the needle entry site clean after you go home.

Finally, if you have any bleeding disorders, or if you are taking blood-thinning medications like warfarin or aspirin, be sure you tell your doctor prior to the test.

How Does the Test Detect the Virus?

When a virus infects the body, the immune system goes to work to fight it off. This is your body’s protective reaction, and it includes the release of certain "antibodies" or "fighter cells" charged with going after the viral cells.

The mononucleosis test looks for the presence of two antibodies that typically form when certain infections—like those caused by the Epstein-Barr virus—are present in the body. Lab technicians place the blood sample on a microscope slide, mix it with other substances, and then watch to see if the blood begins to clump. If it does, the test is considered a positive confirmation of mononucleosis.

What Does a Positive Result Mean?

A positive test result simply means that the antibodies were present in your blood and that, most likely, you are infected with the virus. On rare occasions, however, the test may show antibodies, but you may not be infected. This may occur especially if you have hepatitis, leukemia, Rubella, systemic lupus erythematosus, or other infectious diseases and some cancers.

If the test comes back negative, it may mean you are not infected—or it may mean that the test was performed too early or too late to detect the antibodies. Your doctor might recommend a second test in a couple weeks or may try other tests to confirm the diagnosis.

If your doctors determine you have mononucleosis, they will likely tell you to rest, drink plenty of fluids, and take analgesics to lower a fever, if present. Unfortunately, there are currently no specific medications to treat the infection.

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