The normal adult red blood cell volume distribution width (RDW) is <0.15 (<15%). When the red blood cell volume distribution width is higher than the range of normal values it is called high red blood cell volume distribution width. The higher the red blood cell volume distribution width, the different shapes and sizes of red blood cells in the sample. However, RDW analysis is for reference only and should not be interpreted independently or mechanically. Red blood cell volume distribution width (RDW) is usually used together with mean red blood cell volume (MCV) for morphological classification of anemia. If the mean erythrocyte volume is also increased when the RDW is increased, the anemia is large-cell non-homogeneous, such as megaloblastic anemia and myelodysplastic syndrome. cell non-homogeneous anemia, such as iron deficiency anemia. Therefore, high erythrocyte volume distribution width only indicates that the sample blood erythrocytes vary in shape and size, and cannot be interpreted independently. The specific cause needs to be further clarified in conjunction with the medical history and other relevant laboratory tests for diagnosis and treatment.