What percentage of total blood volume is comprised of erythrocytes, leukocytes, and thrombocytes?

• A. 15%
• B. 25%
• C. 45%
• D. 55%

Answer: (C)

Blood is made up of plasma and formed elements. The formed elements—erythrocytes, leukocytes, and thrombocytes—account for about 45% of blood volume. Most of this portion comes from erythrocytes, while leukocytes and thrombocytes together contribute only a small amount, roughly 1% of the blood. Plasma makes up the remaining ~55%. So the total percentage of blood volume occupied by erythrocytes, leukocytes, and thrombocytes is about 45%.