What is being tested?
The mono test detects heterophile antibodies, which are made by the body in response to an infection by Epstein-Barr virus (EBV). EBV is very common. According to the National Center for Infectious Diseases (NCID), as many as 95% of people in the United States will have been infected by EBV by the time they are 40 years old. It is spread from person to person through the saliva during close contact. Most of the time, the infection occurs in childhood and causes few or no symptoms, but when it first occurs in adolescence, it can cause infectious mononucleosis (mono) in about half of those infected. Although anyone can have mono, most cases of it are found in adolescence and its prevalence is highest in populations of young people, such as are found at high schools, colleges, or in the military.

Mononucleosis is usually a self-limiting condition. It is characterized by the presence of atypical white blood cells (usually reported as reactive lymphocytes), heterophile antibodies, and EBV antibodies in an infected person. Patients who have mono typically have a fever, sore throat, swollen glands, and fatigue. Many will also have an enlarged spleen and a few may have an enlarged liver. Symptoms of the infection usually arise about one month after infection and may last for several weeks. The associated fatigue may last for several months.

About 70%–80% of patients with mono produce heterophile antibodies. These proteins are not specific for EBV but, when found in adolescents in conjunction with mono symptoms, are a good screen for EBV infection.

How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.