Which blood cell type is depressed most severely by bone marrow radiation?

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

Answer: (D)

Radiation damage in the bone marrow mainly hits cells that are actively dividing, and among circulating blood cells, lymphocytes are the most radiosensitive. Because they turnover rapidly and are highly dependent on marrow production, lymphocytes drop quickly and severely after marrow irradiation, leading to marked lymphopenia. In contrast, mature erythrocytes are less affected initially since they are not dividing, and while neutrophils and platelets also fall as marrow function is suppressed, their decline is typically not as dramatic as that of lymphocytes in the acute phase. Thus, lymphocytes are the blood cell type most profoundly depressed by bone marrow radiation.