The diagnosis of infectious mononucleosis (kissing disease) typically involves a combination of various laboratory findings. A complete blood count (CBC) and blood smear provide important diagnostic clues; in the majority of patients, the percentage of atypical T lymphocytes, which develop in reaction to infected B cells, is observed to be greater than 10%. Additionally, 80-90% of patients may show elevated liver function tests (2-3 times the normal range), and 5-10% may experience a decrease in platelet count (thrombocytopenia), responsible for blood clotting. As an aid in diagnosis, the positivity of the monospot test, which detects heterophile antibodies developed during the infection, is important. However, it should be noted that the monospot test can be negative in the early stages of the disease or yield false-positive results in certain conditions like hepatitis or lymphoma. For a definitive diagnosis, serological tests detecting IgM and IgG class antibodies against the virus-specific viral capsid antigen are used.