Determining the hematocrit (Hct). There are two ways to determine the hematocrit (Hct), which is expressed as a percentage of whole blood volume. Top: The first method is a direct measurement that involves centrifuging anticoagulated blood in a microcentrifuge, measuring the heights of the packed red blood cell layer and whole blood (total cell + plasma) in the tube placed vertically, and then dividing the height of the packed red blood cell column by the total height of the blood sample. This method is sometimes called the “spun” Hct or the microhematocrit. Bottom: The second, and far more common approach is to calculate the Hct from red cell count and mean cell volume (MCV) (Hct = red cell count x MCV). The latter 2 values are measured directly by most automated counters/hematology analyzers. Some of the newer analyzers can also measure Hct directly. Spun hematocrit is not recommended due to the low accuracy. Automated analyzers provide more accurate and stable results.
