Mononucleosis tests are blood tests that look for antibodies to the Epstein-Barr virus (EBV) that causes mononucleosis (mono). The antibodies are made by the immune system to fight the infection.

Mono tests include:

• Monospot test (heterophil test). This quick screening test detects a recent mono infection. A sample of blood is placed on a microscope slide and mixed with other substances. If mono is present, the blood clumps (agglutinates). Monospot testing can usually detect antibodies 2 to 9 weeks after a person is infected. It generally is not used to diagnose mono that started more than 6 months earlier.
• EBV antibody test. For this test, a sample of blood is mixed with a substance that attaches to antibodies against EBV. A series of tests can detect different types of antibodies to help determine whether you were infected recently or sometime in the past. Newer tests quickly identify EBV on genetic material other than blood.