A patient with mononucleosis would most likely have which blood finding?

A patient with mononucleosis would most likely have which blood finding?

• A. Lymphocytosis
• B. Eosinophilia
• C. Leukocytosis
• D. Monocytosis

Answer: (A)

In mononucleosis, the immune response drives a prominent rise in lymphocytes in the blood, known as lymphocytosis. You often see many atypical or reactive lymphocytes as CD8+ T cells expand to control EBV-infected B cells. This pattern—lymphocytosis with atypical lymphocytes—is the hallmark you’d expect. Eosinophilia isn’t typical and is more linked to allergies or parasitic infections; monocytosis can occur in some chronic infections but isn’t the characteristic finding here; a generic leukocytosis can occur, but it’s the lymphocyte-predominant pattern that best fits mono.

In mononucleosis, the immune response drives a prominent rise in lymphocytes in the blood, known as lymphocytosis. You often see many atypical or reactive lymphocytes as CD8+ T cells expand to control EBV-infected B cells. This pattern—lymphocytosis with atypical lymphocytes—is the hallmark you’d expect. Eosinophilia isn’t typical and is more linked to allergies or parasitic infections; monocytosis can occur in some chronic infections but isn’t the characteristic finding here; a generic leukocytosis can occur, but it’s the lymphocyte-predominant pattern that best fits mono.