Erythrocytes are the most numerous organic component of blood and also the most important medium for oxygen transport through blood in vertebrates. The width of the red blood cell volume distribution is a parameter obtained by the blood cell analyzer and reflects the uniformity of the red blood cell volume in peripheral blood, and expresses the degree of uniformity of the red blood cell volume size with a reference value of 11.5%-14.5%. This parameter is reduced if the erythrocyte volume is uniform in size. If the erythrocyte distribution width is low, it indicates that the erythrocytes are more neatly distributed than in normal subjects. If the erythrocyte volume is not uniform in size and varies widely, this parameter is higher than the reference value. If the erythrocyte distribution width is simply low, it is not clinically significant and can be temporarily observed in the absence of other abnormal symptoms. If there is significant anemia, thalassemia needs to be considered and further examination by a specialist at a hospital.