Low white blood cells and red blood cells means that the number of both white blood cells and red blood cells are lower than the normal range. This condition is very common in clinical practice, and the most common causes are: i. Female patients who suffer from iron deficiency anemia and have chronic inflammatory conditions at the same time will have a decrease in both red blood cells and white blood cells, and after iron supplementation and anti-inflammatory treatment, the number of red blood cells and white blood cells will gradually increase. Patients with simple severe iron deficiency anemia, due to long-term severe iron deficiency anemia, will also have a decrease in the number of red blood cells and white blood cells, and sometimes even a decrease in the number of platelets as well. Third, patients with severe megaloblastic anemia end up with low white blood cells and red blood cells due to a long-term deficiency of folic acid and vitamin B12 and a lack of raw materials needed for blood cell production in various blood cells. Patients with aplastic anemia, which is a bone marrow hematopoietic failure disease, will also have low red blood cells and white blood cells due to the failure of bone marrow hematopoietic function and reduced ability to produce blood cells.