Which blood cell type is depressed most severely by radiation?

• A. Erythrocytes
• B. Platelets
• C. Neutrophils
• D. Lymphocytes

Answer: (D)

Lymphocytes are the most radiosensitive blood cells. Ionizing radiation damages DNA, and lymphocytes have a high nucleus-to-cytoplasm ratio with limited capacity to repair DNA damage, so they undergo apoptosis readily after exposure. This makes their counts fall rapidly and more severely than other circulating cells.

Erythrocytes are mature and not dividing, so they’re relatively resistant to immediate radiation effects. Platelets relate to bone marrow activity but their decline reflects marrow suppression over time, not an immediate, severe drop. Neutrophils also decrease after radiation but not as dramatically or as quickly as lymphocytes in the acute phase.