An increase in the width of the erythrocyte volume distribution is seen in iron deficiency anemia. In particular, an increase in the width of the erythrocyte volume distribution when the MCV is still in the reference range is characteristic of early iron deficiency anemia. Erythrocyte volume distribution width is a parameter that reflects the heterogeneity of erythrocyte volume size and is often measured as a coefficient of variation of the measured erythrocyte volume size. It is a parameter that reflects the heterogeneity of the volume of peripheral blood erythrocytes obtained by the hematology analyzer. In short, it is an objective indicator of the heterogeneity of red blood cell size. The morphological classification of anemia is generally performed by two parameters, RDW and MCV. Differential diagnosis of increased erythrocyte volume: 1. High erythrocyte pressure volume: The erythrocyte pressure volume helps to understand the increase and decrease of erythrocytes. When the absolute value of erythrocytes is increased due to various causes, there is a corresponding increase in erythrocyte pressure volume. The high erythrocyte pressure product is found in the routine blood tests after the patient is in shock. 2, erythrocyte malformation: erythrocyte malformation in the clinical more suggestive of glomerulonephritis, urine erythrocyte morphological examination is a more widely used clinical method in the last decade or so. The basic principle is that red blood cells of glomerular origin often undergo morphological aberrations due to mechanical damage to the glomerular basement membrane and/or changes in the intrarenal osmotic pressure gradient, while the morphology of urinary red blood cells in non-glomerular hematuria generally does not undergo the above changes and shows homogeneous orthomorphism. This can help distinguish glomerular hematuria from non-glomerular hematuria. 3, red blood cells are in the shape of money strings: red blood cells are arranged in money strings because the area of oxygen exchange in the plasma is small, resulting in oxygen deficiency in the blood, increased plasma viscosity, slow blood flow, aggravating the lack of oxygen supply to the whole body tissues, so that the entire microcirculation is significantly impaired.