Mean red blood cell volume, abbreviated as MCV, is the average volume of individual red blood cells in the body, measured in fl, and is usually calculated indirectly. The reference value for mean red blood cell volume in normal subjects is 82-100 fl. Mean red blood cell volume is indicated for the diagnosis and treatment of various anemia disorders. Physiological variants, elevated, can occur and can be seen in newborns, pregnancy, alcohol consumption, intense muscular activity such as oral contraceptives. infants before 6 months of age, may cause a decrease in mean red blood cell volume. Pathological variation, mainly used in the diagnosis and treatment of various anemias, macrocytic anemia, that is, MCV greater than 100fl, is mainly seen in deficiencies of folic acid and vitamin B12, such as megaloblastic anemia, nutritional megaloblastic anemia, and pernicious anemia of pregnancy. Normocytic anemia with MCV of 82-100fl is due to a decrease in hemoglobin and red blood cell count balance, such as acute blood loss, aplastic anemia, leukemia, etc. Small cell anemia alone, with MCV less than 82fl, is mostly seen in chronic infections and poisoning, such as uremia, liver disease, rheumatic diseases, and malignant tumors. Small cell hypochromic anemia with MCV less than 82fl, such as chronic blood loss anemia, iron deficiency anemia, etc.