A decrease in red blood cells in the peripheral blood indicates the occurrence of anemia. There are three causes of red blood cell reduction: the first cause is a decrease in red blood cell production: this can be caused by a variety of reasons, the most common being disorders of red blood cell production, such as aplastic anemia, pure red aplastic anemia, and acute leukemia, multiple myeloma, myelodysplastic syndrome, and metastatic cancer of the bone marrow. Also, a lack of hematopoietic raw materials, such as iron deficiency, lack of folic acid and vitamin B12, can cause a decrease in the number of red blood cells; the second is excessive destruction of red blood cells in the peripheral blood: the most common cause is autoimmune hemolytic anemia. In addition, patients with thalassemia and sericosis, also have a reduced number of red blood cells. The third condition is red blood cell loss. Red blood cell loss can be seen in chronic blood loss in patients with hemorrhoids and in women with excessive menstruation, as well as in peptic ulcers and digestive tract tumors, which can cause a decrease in the number of red blood cells.