Hematopoietic ARS occurs at which dose threshold?

• A. 0.5 Gray (Gy)
• B. 1 Gray (Gy)
• C. 10 Gray (Gy)
• D. 50 Gray (Gy)

Answer: (B)

Hematopoietic ARS happens when radiation injures the bone marrow’s stem cells, so the body can’t produce enough blood cells—white cells, platelets, and red cells—leading to infection risk, bleeding, and anemia. The minimum dose that reliably produces this hematopoietic injury is about 1 Gray. Doses around 0.5 Gy may cause some mild marrow changes but don’t trigger the clear hematopoietic syndrome. At about 1 Gy, you start to see significant suppression of blood cell production, with symptoms like increased infections and bleeding that can appear days to weeks after exposure. Higher doses, around 10 Gy, push the body into GI syndrome with severe gastrointestinal damage, and much higher doses (tens of Gy) lead to rapid multi-organ failure, including CNS effects. So 1 Gy is the appropriate threshold for hematopoietic ARS.