The number of red blood cells in normal human peripheral blood is 4-5.5 million/mL for adult males and 3.5-5 million/mL for adult females, if it is lower than the normal range it is a low red blood cell level. The most common cases of low erythrocyte count are: first, after drinking a lot of water, a lot of transfusions, resulting in an increase in plasma volume, blood dilution, and a decrease in red blood cells. If too much water is expelled from the body, the red blood cell count will return to normal. Second, the most common type of low red blood cell count is anemia, whether it is various types of anemia, such as aplastic anemia, iron deficiency anemia, megaloblastic anemia, hemolytic anemia, thalassemia, etc., the number of red blood cells will be low. In this case, it is necessary to go to the hospital for routine blood tests to clarify the type of anemia and give the corresponding treatment according to the type of anemia. Iron deficiency anemia can be treated with iron supplements and vitamin C. After a period of treatment, the number of red blood cells will gradually return to normal.