A patient diagnosed with mononucleosis would most likely exhibit which laboratory finding?

In the context of mononucleosis, particularly when caused by the Epstein-Barr virus (EBV), it is common to see lymphocytosis as a significant laboratory finding. Lymphocytosis refers to an elevated level of lymphocytes, which are a type of white blood cell that plays a crucial role in the immune response.

Mononucleosis is characterized by fever, sore throat, fatigue, and swollen lymph nodes, and the body responds to the viral infection by increasing the production of lymphocytes. These increased lymphocyte levels are primarily due to atypical lymphocytes, which can be identified in a complete blood count (CBC) during diagnosis.

Understanding the pathophysiology of mononucleosis helps clarify why an elevation in lymphocyte count is expected. The body's immune response mobilizes lymphocytes to fight off the viral infection, leading to the observed lab finding of lymphocytosis in affected patients. This makes lymphocytosis not only a hallmark of mononucleosis but also a key indicator for medical professionals when considering a diagnosis.