What percentage of blood can be drawn from an adult in 24 hours?

• A. 1-5%
• B. 6-10%
• C. 11-15%
• D. 16-20%

Answer: (A)

The concept being tested is safe blood loss relative to a person’s total blood volume. In a healthy adult, total blood volume is about 7–8% of body weight, roughly 5 liters for a 70 kg person. Medical guidelines generally allow drawing up to about 5% of this volume within 24 hours without causing significant circulatory problems, which is about 250 mL. Drawing more than that in a day increases the risk of hypovolemia and dizziness or worse, especially if there are other losses or underlying conditions. Therefore, 1–5% is the safe, typical range for blood drawn in a 24-hour period. If larger amounts are needed, clinicians coordinate carefully and consider the patient’s health status.