Diagnosis

Physical exam

Your doctor may suspect mononucleosis based on your signs and symptoms, how long they've lasted, and a physical exam. He or she will look for signs such as 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.