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

Mononucleosis is a viral infection 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. Symptoms may last from several weeks to a couple of months. In rare cases, it can last several months.

Symptoms of mononucleosis include:

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

If you have these symptoms for a week or longer, you may have mono. Your doctor may perform the mononucleosis spot test to confirm (or rule out) the diagnosis.

When a virus infects the body, the immune system goes to work to fight it off. This is your body’s protective reaction. 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.

This procedure is most often done once symptoms have developed, which is typically 4 to 6 weeks after exposure (delay is referred to as incubation period). The test helps to confirm a diagnosis of the illness. Like most blood tests, it’s performed by a doctor or healthcare professional (such as a nurse) who draws 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.)

Your doctor will wrap an elastic band around your upper arm to make the vein fill with blood. They’ll then gently insert a small needle into the vein, allowing the blood to flow into an attached tube. When the tube contains enough blood, your doctor will withdraw the needle and cover the small puncture wound with a bandage.

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

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

Other complications may include soreness at the injection site, particularly if your doctor or nurse 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. 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. A warm compress may help if you notice any swelling.

As with all procedures that create an opening in the skin, there is a rare chance of infection. Your doctor 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 before the test.

A positive test result means that the antibodies charged with attacking the Epstein-Barr virus were detected in your blood, and that you are mostly likely infected with the virus. On rare occasions, the test may show antibodies even though 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 doctor determines you that have mononucleosis, they will likely tell you to rest, drink plenty of fluids, and take analgesics to lower a fever. Unfortunately, there are currently no specific medications to treat the infection.