The hematocrit is the volume of all blood cells in the blood as a percentage of the total blood volume. In peripheral blood, red blood cells are the most numerous, so hematocrit is primarily an effect of the number of red blood cells. The hematocrit in adult men is 40%-50%; in adult women it is 37%-48%. If there is a significant increase or decrease in the number of red blood cells, the hematocrit will fluctuate significantly, for example, in various types of anemia, such as iron deficiency anemia, aplastic anemia, megaloblastic anemia, hemolytic anemia, thalassemia, etc. A significant decrease in blood cell pressure volume can occur. If there is an increase in the number of red blood cells, such as true erythrocytosis, primary thrombocytosis, and various chronic hypoxic diseases, the hematocrit will be significantly increased. Therefore, hematocrit is mainly an effect of increased or decreased number of red blood cells.