Erythrocyte pressure volume, also called erythrocyte specific volume, is the percentage of the volume of red blood cells in peripheral blood to the volume of blood. Because erythrocyte pressure volume is a percentage, it is influenced by multiple relationships between the volume size of the red blood cell count itself and the plasma volume. If the number of red blood cells is severely reduced, the erythrocyte pressure volume will be significantly low due to the reduction of molecules, which is common in various anemic diseases, and the more severe the anemia, the lower the erythrocyte pressure volume will be. If there is a significant increase in the number of red blood cells, there will also be a significant increase in the erythrocyte pressure product. Also, if there is severe dehydration, such as profuse sweating, severe diarrhea, vomiting, etc., even if the red blood cell count does not increase, a significantly higher erythrocyte pressure product may occur due to a decrease in plasma volume, i.e., a narrowing of the denominator.