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How is Mono Diagnosed?


Updated May 01, 2014

Question: How is Mono Diagnosed?

Mono is short for mononucleosis or infectious mononucleosis. It is generally caused by the Epstein-Barr virus (EBV) or cytomegalovirus (CMV).

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 mono.

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.

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 he looks in the back of your throat, feels your neck and other areas where you may have swollen lymph nodes, and listens to your lungs. If the doctor suspects mono, he will likely order a mono spot test. Additionally, they may test to see if your white blood cell count is elevated.

A mono spot test involves drawing your blood. The blood is usually taken out of a vein in your arm. While somewhat uncomfortable, like a shot, the pain only lasts for a minute. Not enough blood is taken to make you anemic but, especially if you are squeamish, it's best to eat or drink something before having your blood drawn for this 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 mono spot test is "positive." A positive mono spot test accompanied by the symptoms of mono results in a diagnosis of infectious mononucleosis. However, mono spot tests can be false-positive, about 10-15% of the time.

Also, rarely, people who actually have mono can have a negative mono spot test. This may happen because 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. It may also mean that you are not infected with EBV but have developed "mono" (some doctors believe it is more accurate to call this a "mono-like" infection) from cytomegalovirus.

If your mono spot test is negative but you have all the symptoms of mono, more testing will be needed to make a diagnosis.

Since EBV is a virus, not a bacteria, mono cannot be treated with antibiotics. 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.


CDC. Epstein-Barr Virus and Infectious Mononucleosis. Accessed: August 30, 2011 from http://www.cdc.gov/ncidod/diseases/ebv.htm

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