The Heterophile Antibody Test is a blood test used to detect the presence of heterophile antibodies, which are often produced in response to infections like mononucleosis. This test is particularly useful for diagnosing infections caused by the Epstein-Barr virus. When a person is infected, their immune system creates these antibodies, which can be identified in a blood sample. The test is simple and typically involves drawing a small amount of blood. Results can help doctors determine if a patient has mononucleosis or other related illnesses. A positive result usually indicates an active infection, guiding further treatment and care.