Infectious Mononucleosis

Diagnosis

Your doctor will ask you about your medical history and current symptoms, as well as about your recent exposure to anyone with mononucleosis or mono-like symptoms.

During a physical exam, your doctor will look for signs of mononucleosis, especially fever, a reddened throat with enlarged tonsils (possibly covered with pus), swollen lymph nodes in the neck and elsewhere, an enlarged spleen (located in the upper left side of the abdomen) and a red rash, usually on the chest.

Your doctor also will do blood tests to help make the diagnosis. The results of these blood tests may not be abnormal until the person has been ill for a week. There are two types of tests that help make the diagnosis:

• Differential white blood cell count – This test identifies the numbers of each different type of white blood cell circulating in your blood. In the first few weeks of mono, the number of lymphocytes (a type of white blood cells) and particularly the number of lymphocytes with an unusual appearance, called atypical lymphocytes, are quite high. While other conditions can raise the number of lymphocytes, few other conditions produce atypical lymphocytes.

• Heterophil tests – Mononucleosis causes white blood cells to make an unusual kind of antibody called heterophil antibody. Few other conditions cause this antibody to be produced. It can be measured using several different tests. The traditional heterophil test usually takes 1-2 days. Newer tests, such as the Mono Spot test, give more rapid results, without sacrificing accuracy. For that reason, they are the tests most often used.

Expected Duration

Symptoms of mononucleosis usually are most intense during the first two to four weeks of the illness. However, mononucleosis symptoms, especially fatigue, can sometimes last for several months.