The Epstein-Barr virus is also known as mononucleosis and is considered a member of the herpes virus family. Most people will become infected with this virus at some point in their lives, but will suffer only mild symptoms. Infection during adolescence or young adulthood causes mononucleosis about 1/3 to 1/2 of the time. 

This condition is more serious, with fever, swollen lymph glands, sore throat and general malaise. It can last for one to two months and stays dormant in the body for the rest of the patient's life. It can then reactivate later in life, often without signs of illness, in order to infect others. Only people with compromised immune systems are in danger from this reactivated virus. In a very few carriers, rare cancers such as nasopharyngeal carcinoma or Burkitt's lymphoma occur. 

Tests are most likely to be required when someone has symptoms that suggest mononucleosis, but a negative mono test. An EBV test can also help pregnant women with flu-like symptoms find out if they have the virus. Some EBV tests will show antibodies in people who have previously had the disease but are no longer suffering from it. These people tend to have IdG antibodies, but not IgM antibodies.