Erythrocyte distribution width is to reflect the heterogeneity of the volume size of red blood cells, the normal range is 10~16%, the low erythrocyte distribution width indicates that the size of red blood cells is more consistent, it may be pathological anemia or physiological fluctuations, which need to be analyzed specifically. 1. Anemia: In iron deficiency anemia, the red blood cell size will become smaller; while in megaloblastic anemia, the red blood cell size will become larger. When the volume of red blood cells becomes smaller or larger in a consistent manner, the width of red blood cell distribution may be low, and symptoms such as fatigue and dizziness may occur, which need to be combined with hemoglobin content, ferritin and other inspection indexes to assist in a clear diagnosis. 2. Physiological: low red blood cell distribution width indicates that the size of red blood cells is relatively consistent, and it is not necessarily a pathologic change, which needs to be reviewed regularly. Low erythrocyte distribution width may be physiologic or pathologic, and requires regular review and timely consultation if necessary.