How is mono diagnosed?
A diagnosis of mono is suspected by the doctor based on the patient's symptoms and signs. Mono is confirmed by blood tests that may also include tests to exclude other possible causes of the symptoms, such as tests to rule out Strep throat. Early in the course of mono, blood tests may show an increase in one type of white blood cell (lymphocyte). Some of these increased lymphocytes have an unusual or "atypical" appearance when viewed under a microscope, which suggests mono.
More specific blood tests, such as the monospot and heterophile antibody tests, can confirm the diagnosis of mono. These tests rely on the body's immune system to make measurable antibodies against the EBV. Unfortunately, the antibodies may not become detectable until the second or third week of the illness. A blood chemistry test may reveal abnormalities in liver function.