If your body detects EBV, it can develop a type of antibody called heterophile antibodies. If you have heterophile antibodies in your blood, then your monospot test is positive.. A positive monospot test accompanied by the symptoms of mono results in a diagnosis of infectious mononucleosis. However, monospot tests can be false-positive, about 10-15% of the time, particularly in early stages of the illness. You may also receive a negative monospot test even if you have mono.