Physical exam

Your doctor may suspect mononucleosis based on your signs and symptoms, how long they've lasted and a physical examination. He or she will look for signs like swollen lymph nodes, tonsils, liver or spleen, and consider how these signs relate to the symptoms you describe.

Blood tests

• Antibody tests. If there's a need for additional confirmation, a monospot test may be done to check your blood for antibodies to the Epstein-Barr virus. This screening test gives results within a day. But it may not detect the infection during the first week of the illness. A different antibody test requires a longer result time, but can detect the disease even within the first week of symptoms.
• White blood cell count. Your doctor may use other blood tests to look for an elevated number of white blood cells (lymphocytes) or abnormal-looking lymphocytes. These blood tests won't confirm mononucleosis, but they may suggest it as a possibility.