Which of the following laboratory findings is commonly associated with infectious mononucleosis?

The presence of atypical lymphocytes in the complete blood count (CBC) is a hallmark laboratory finding associated with infectious mononucleosis, which is most commonly caused by Epstein-Barr virus (EBV). Atypical lymphocytes are characterized by their larger size and irregular shape, as well as abundant cytoplasm and prominent nuclei. In infectious mononucleosis, these atypical lymphocytes are often reactive T-cells that respond to the viral infection.

This finding is significant as it helps to differentiate infectious mononucleosis from other conditions that may present with similar symptoms, such as other viral infections or even certain hematological conditions. The detection of these atypical lymphocytes is generally accompanied by an increase in the overall lymphocyte count, further supporting the diagnosis.

While other options like hypocytic leukocytosis, a decrease in bilirubin levels, or negative liver function tests do not correlate strongly with infectious mononucleosis. Hypocytic leukocytosis would generally suggest a different hematological process, and a decrease in bilirubin levels is not a typical finding in this condition, where mild elevations in liver enzymes may occur instead. Thus, the presence of atypical lymphocytes is the defining laboratory characteristic that clinicians use to recognize infectious monon