The volume of red blood cells is also defined as hematocrit. After centrifugation of a blood tube, two layers can be seen: the upper phase consists of the plasma, while the red blood cells sink to the bottom of the tube, which is visible as a red layer (Figure 1). White blood cells and platelets settle in the interface between both layers. A low hematocrit value can be an indicator for anemia.
Figure 1: Schematic representation of the determination of the hematocrit.