The causes of high erythrocyte hematocrit include blood system diseases, diarrhea, and decreased lung function. 1. Blood system diseases: such as primary erythrocytosis patients may have high erythrocyte pressure volume, if you can’t follow the doctor’s instructions in time to control the use of medication, it may cause blood clots, and in severe cases, it can cause pulmonary infarction, cerebral infarction and other more serious situations. 2. Diarrhea: diarrhea is serious, if you can not timely replenish water, it is easy to lead to a large amount of water loss. The blood is concentrated, leading to high erythrocyte pressure volume. 3. Reduced lung function: patients with chronic respiratory diseases, as well as patients with asthma disease and chronic bronchitis, can easily lead to reduced lung function and hypoxia, which can lead to high erythrocyte pressure volume. High erythrocyte pressure volume may also be related to other diseases, and should be consulted in time to avoid delay.