Hematocrit, also called hematocrit, is the volume of red blood cells in the peripheral blood as a percentage of the blood volume. Hematocrit is 40%-50% in adult males and 37%-48% in adult females. The most common cause of a lower hematocrit is a decrease in the number of red blood cells, which means that there is anemia. The more severe the anemia, the lower the RBC volume, such as iron deficiency anemia, aplastic anemia, hemolytic anemia, megaloblastic anemia, thalassemia, and so on, will have a significantly lower RBC volume. The most common reason for an increase in erythrocyte volume is an increase in the number of red blood cells, for example, in chronic hypoxic diseases, due to an increase in the concentration of erythropoietin in the body to stimulate the proliferation of red blood cells and an increase in the number of red blood cells, there will be a significant increase in the erythrocyte volume.