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. The following diseases are also causes of increased erythrocyte volume: 1. Sickle cell anemia ocular lesions Sickle cell anemia is a genetic defect of hemoglobin, which can be divided into several types, and the severity of the ocular lesions varies from type to type. 2.Secondary iron granulocytic anemia Secondary iron granulocytic anemia is secondary to treatment with certain drugs or chemical toxicants (such as anti-TB drugs, chlortetracycline, alkylating agents and other anti-cancer drugs and lead, alcohol, etc.) and certain diseases (such as myeloproliferative diseases and tumors, myelodysplasia, anomalous syndromes chronic infections), and the number of ringed iron granulocytes, anemia, and a lighter iron load. 3.Hereditary iron granulocytic anemia Most of the patients with hereditary iron granulocytic anemia are male except for a few typical cases in which anemia appears after birth or in infants, and most of them appear around the age of 10 to 20, and occasionally they are found after 50 to 60 years old. 4. Microangiopathic hemolytic anemia Microangiopathic hemolytic anemia is a severe diffuse thrombotic microangiopathy characterized by microangiopathic hemolytic anemia, depletion of platelet aggregation, and organ damage (such as kidney, central nervous system, etc.) caused by microthrombosis. It is a hemolytic anemia syndrome that occurs due to the fragmentation of red blood cells caused by microangiopathy. 5, traumatic cardiogenic hemolytic anemia The trauma, hemodynamic abnormalities or foreign bodies placed after corrective surgical treatment of heart or macrovascular diseases rub and impact red blood cells, causing mechanical damage, resulting in hemolytic anemia, which belongs to traumatic cardiogenic hemolytic anemia.