Low red blood cell distribution width may be caused by thalassemia, iron deficiency anemia, megaloblastic anemia, etc. It may also be seen in other blood diseases such as aplastic anemia and leukemia. It is necessary to combine with other indicators to make a comprehensive judgment. 1. Thalassemia: Thalassemia is characterized by microcytic hypochromic anemia, which causes the volume of red blood cells to show uniform deformation and the phenomenon of low red blood cell distribution width. 2. Iron deficiency anemia: Low red blood cell distribution width may also occur in iron deficiency anemia, which is an early indication of iron deficiency because the red blood cell distribution width decreases earlier than the red blood cell volume. 3. Megaloblastic anemia: low red blood cell distribution width may also be caused by megaloblastic anemia, due to the uniform increase in red blood cell volume, the situation of low red blood cell distribution width. 4. Other blood diseases: such as aplastic anemia, leukemia, myelodysplastic syndrome and so on, due to the low function of erythropoiesis, resulting in low erythrocyte distribution width. Patients with low erythrocyte distribution width should go to the hospital in time for examination and standardized treatment under the guidance of professional doctors after clarifying the cause of the disease.