What finding indicates infectious mononucleosis in a patient?

The presence of heterophile antibodies is a key indicator of infectious mononucleosis, commonly associated with Epstein-Barr virus (EBV) infection. These antibodies are typically detected through the Monospot test, which identifies heterophile antibodies that react with antigens on the surface of the virus-infected B lymphocytes. Their presence confirms the immune response to the infection and is considered a hallmark diagnostic finding for this condition.

While elevated liver enzymes can occur in infectious mononucleosis due to liver involvement, they are not specific to this condition and could be seen in a variety of liver and non-liver diseases. A positive throat culture would more likely indicate a bacterial infection, such as streptococcal pharyngitis, rather than viral mononucleosis. Normocytic anemia is not typically associated with infectious mononucleosis; while anemia can occur as a secondary complication, it is not a defining diagnostic feature for the condition itself. Thus, heterophile antibodies are the most direct and relevant finding indicating infectious mononucleosis.