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How is Mono Diagnosed?

By Dr. Kristie

Are you feeling tired lately with swollen lymph nodes – and concerned that you might have mono?

Mononucleosis is a common viral infection that most people have been exposed to at one time or other – since over ninety percent of people have antibodies against the Epstein Barr virus that causes this infection. Despite being exposed to the virus, not everyone experiences symptoms.

In some cases, the immune system destroys the virus before it can cause signs of illness. On the other hand, if you’re experiencing symptoms, it’s important to get a diagnosis since, in some cases; people with mono can experience complications such as hepatitis or a ruptured spleen.

How is Mono Diagnosed?: The Typical Symptoms

The classic symptoms of mononucleosis include lymph node swelling, sore throat, low grade fever, and a generalized lack of energy. These symptoms are very mild in some people and more severe in others. Some people also experience a heaviness in their pelvic region due to enlargement of the liver or spleen. If any of these symptoms develop, it’s time to see a doctor.

Testing for Mononucleosis: The Doctor Will See You Now

A doctor can get a rough idea whether you actually have mono based on the clinical exam. A person with mononucleosis may have an inflamed red throat and swollen lymph nodes. Up to half of all people with mono have an enlarged spleen – and some will have liver enlargement.

How is Mono Diagnosed? The Lab Tests

Your doctor may start by taking a throat culture to make sure it’s not a Strep infection - which can give symptoms similar to mono. Once that is ruled out, your doctor will run a monospot test. A monospot test is a quick, 10 min. test that can be run in the office to check for heterophile antibodies which are present in mononucleosis.

The monospot test is usually only positive when there’s an active mono infection and it’s pretty specific for the virus, meaning it gives an accurate diagnosis when it’s positive. On the other hand, it’s not extremely sensitive, so there’s a chance it could miss a person who has active mono.

Because the monospot test isn’t very sensitive, your doctor may order some other blood tests to help confirm the diagnosis. One is a complete blood cell count. A person with mononucleosis often has a decreased white blood cell count - but an increased number of atypical lymphocytes.

These atypical lymphocytes are highly suggestive, but not diagnostic for mono. Your doctor will probably also do a blood test to check liver enzymes to make sure there isn’t liver involvement too.

A small number of people won’t have the characteristic antibodies that cause the monospot test to turn positive which makes the diagnosis more difficult. In this case, your doctor may want to draw additional antibody tests to clinch the diagnosis.

Testing for Mononucleosis: The Bottom Line?

The diagnosis of mono can usually be made based on clinical exam and the results of a complete blood count and monospot test. In some cases, additional antibody tests may be needed.


  • Merck Manual. 18th edition.
  • J. Clin. Pathol. 22 (3): 324–5.

About the Author

She is a Medical Doctor with a concentration in Family Practice. She also has an undergraduate degree in both Biology and Psychology and masters in Clinical Pathology.

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