In which condition would lymphocyte count be notably elevated?

Mononucleosis, often caused by the Epstein-Barr virus, is characterized by an elevated lymphocyte count, specifically atypical lymphocytes. This condition triggers the immune system's response, leading to an increase in lymphocytes as the body fights off the viral infection. Elevated lymphocyte counts are a hallmark finding in the laboratory evaluation of patients with mononucleosis and are part of the reason the diagnosis often includes symptoms such as fatigue, sore throat, and swollen lymph nodes.

In contrast, other conditions listed may not show a significant elevation in lymphocytes. Acute bacterial infections typically cause an increase in neutrophils rather than lymphocytes. Chronic obstructive pulmonary disease is more related to respiratory issues and inflammation but does not specifically lead to a notable increase in lymphocytes. Aplastic anemia involves a decrease in blood cell production, including lymphocytes, rather than an elevation. Therefore, the increase in lymphocytes in mononucleosis is a key differentiator that confirms this as the correct choice.