Hematocrit

Hematocrit, also known as erythrocyte volume fraction, is the blood volume which is occupied by red blood cells. In other words, hematocrit measures how much space in the blood is occupied by red blood cells. It is useful when evaluating a person for anemia. It gives a percentage of red blood cells found in whole blood. It is normally about 48% for men and 38% for women. Hematocrit is an integral part of a person's complete blood count results, along with hemoglobin concentration, white blood cell count, and platelet count.

Blood drawn from someone is put in a small capillary tube, which is then spun in a small centrifuge at 10,000 RPM for five minutes. As the tube spins, the red blood cells go to the bottom of the tube, the white blood cells cover the red in a thin layer called the buffy coat, and the liquid plasma rises to the top. The spun tube is examined for the line that divides the red cells from the buffy coat and plasma. The height of the red cell column is measured as a percent of the total blood column. The higher the column of red cells, the higher the hematocrit.