Mononucleosis Spot Test (Monospot Test)

Blood Tests to Diagnose Infectious Mononucleosis

Drawing blood
Drawing blood. Francis Twitty/Getty Images

The mononucleosis spot test, better known as the monospot test, is a diagnostic test for mono (short for infectious mononucleosis). The monospot test is a rapid heterophile antibody test that typically has results within 72 hours. Your doctor will generally have this test done along with a CBC (complete blood count) which requires your blood to be drawn from your vein. However this test can also be done as a finger poke.

Mono is generally caused by the Epstein-Barr virus (EBV), however cytomegalovirus (CMV) can cause a CMV mononucleosis, which has similar symptoms. While the CDC no longer recommends the monospot test, many guidelines still encourage the test to help identify the cause of mono.

Symptoms Related to Mono

Mono typically causes severe fatigue (tiredness or lethargy), swollen tonsils with a very sore throat, swollen lymph nodes, fever, and sometimes body aches. It is most common in adolescents, although many people become infected with EBV and never develop infectious mononucleosis.

If you suspect you have mono, you should see your physician to be tested and rule out other illnesses, such as strep throat, which must be treated with antibiotics.

Diagnosing Mono

Your doctor will look at your symptoms and your age (since people infected with EBV are more likely to develop mono if they are a teenager or young adult), and perform a physical evaluation where they will look in the back of your throat, feel your neck and other areas where you may have swollen lymph nodes, and listens to your lungs.

Your doctor will usually order a CBC and monospot test.

If you have mono, your CBC will typically show an elevated White Blood Count (WBC), specifically lymphocytes. Your doctor may tell you that you have lymphocytosis, which just means that your lymphocytes are elevated. Your lymphocytes are just a part of your body's immune system.

It is natural for these cells to be elevated during an infection. You will also have a positive monospot test.

Monospot Test

Your blood will be analyzed in a laboratory for antibodies. Antibodies are a specific component of your immune system that fight infection. Your body produces these antibodies in response to a virus or other pathogen that it considers a threat. If your body detects EBV, it can develop a type of antibody called heterophile antibodies. If you have heterophile antibodies in your blood, then your monospot test is "positive." A positive monospot test accompanied by the symptoms of mono results in a diagnosis of infectious mononucleosis. However, monospot tests can be false-positive, about 10-15% of the time, particularly in early stages of the illness.

You may also receive a negative monospot test even if you have mono. If you are tested within the first week of symptom onset, you stand approximately 25% chance of having a negative test result. This may also happen if you waited too long to see a doctor, and the heterophile antibodies rapidly decrease in number after you've been infected for about four weeks.

You may also have mono from a different virus than EBV, such as CMV. Some doctors may refer to CMV mononucleosis as a "mono-like" infection and reserve the term "mono" for EBV infectious mononuclosis.

If your monospot test is negative but you have all the symptoms of mono, your doctor will likely repeat the monospot test before doing more extensive antibody tests. These more specific EBV antibody tests are rarely needed, but may include the heterophile antibody, cytomegalovirus, or Toxoplasma antibody test.

Since EBV is a virus, not a bacteria, mono cannot be treated with antibiotics, but rather the mono symptoms are treated. Rest and fluids are highly recommended, and in some cases, your doctor may send you home with a prescription to treat symptoms of sore throat and swollen lymph nodes.

Source:

Aronson, M.D. & Auwaerter, P.G. (2015). Infectious mononucleosis in adults and adolescents. Accessed on January 1, 2017 from http://www.uptodate.com (subscription required)

CDC. Epstein-Barr Virus and Infectious Mononucleosis. Accessed: January 1, 2017 from https://www.cdc.gov/epstein-barr/laboratory-testing.html

Chernecky, CC & Berger, BJ. (2013). Laboratory Tests and Diagnostic Procedures. 6th ed. Philadelphia: WB Saunders.

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