The hematocrit value reflects the proportion of blood comprised of which element?

• A. Platelets
• B. Red Blood Cells
• C. White Blood Cells
• D. Plasma

Answer: (B)

Hematocrit is the percentage of blood volume made up by red blood cells. When blood is spun in a centrifuge, plasma rises to the top, a small buffy coat contains white blood cells and platelets, and red blood cells form the bottom layer. The hematocrit is the proportion of the total volume that those bottom red cells occupy, so red blood cells are the correct focus. Platelets and white blood cells are only a small part of the blood volume in the buffy coat, and plasma is the liquid portion not counted in hematocrit.