The width of the red blood cell volume distribution is a parameter that reflects the heterogeneity of the red blood cell volume size, often as a coefficient of variation of the measured red blood cell volume size. It is a parameter that reflects the heterogeneity of the volume of peripheral blood erythrocytes obtained by hematology analyzer measurements. 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. The diagnosis of increased erythrocyte volume is based on the following: 1. ID (1) serum ferritin <12 mg/L; (2) bone marrow iron staining shows the disappearance of small stainable iron particles and less than 0,15 iron granulocytes; (3) hemoglobin and serum iron are still normal. 2, IDE (1) ID (1) + (2); (2) transferrin saturation <0, 15; (3) FEP/Hb>4, 5mg/gHb; (4) hemoglobin is still normal. 3, IDA (1) IDE of (1) + (2) + (3); (2) small cell hypochromic anemia: male <120g/L, female <110g/L, pregnant women Hb <100g/L; MCV <80fl, MCH <27pg, MCHC <0, 32. 4, should emphasize the etiological diagnosis Only if the etiology is clear, IDA can be eradicated; sometimes the cause of iron deficiency is more serious than anemia itself is more serious. For example, IDA due to gastrointestinal malignancy with chronic blood loss or postoperative residual cancer of the stomach, fecal occult blood should be checked several times, and if necessary, gastrointestinal X-ray or endoscopy; for menstruating women, should be checked for gynecological diseases.