High mean red blood cell volume means that the mean red blood cell volume is more than 100 fl. Under normal circumstances, the mean red blood cell volume ranges from 80.0 to 93.6 fl for men and 77.7 to 93.7 fl for women. The mean red blood cell volume plays an important role in the diagnosis and treatment of various anemias, and the causes of high mean red blood cell volume include physiological and pathological causes. 1. Physiological causes: physiological high mean red blood cell volume is common in newborns, pregnant women or women taking oral contraceptives, which is a normal physiological phenomenon and does not require special treatment. 2. Pathological causes: Pathologically high mean red blood cell volume is commonly caused by vitamin B12 and folic acid deficiency, such as megaloblastic anemia, nutritional megaloblastic anemia, aplastic anemia and so on. Vitamin B12 and folic acid can be supplemented under doctor’s supervision, and regular review can be done to monitor the recovery. When there is a high mean red blood cell volume, the patient should do the next examination under the guidance of the doctor to clarify the cause of the disease and treat the cause.