an increase in the total quantity of blood in the human body. A distinction is made between polycythemia vera, in which the increase in erythrocytes, up to 8–10 million in 1cu mm of blood, is greater than the increase in the total volume of blood plasma, and hypervolemia, which is characterized chiefly by an increase in the volume of plasma. The latter may be of cardiac origin or may be due to water retention in the vascular system after copious drinking. The normal ratio of the volume of blood cells to that of plasma is 45:55.
an increase in the number of erythrocytes in the blood. Spurious, or relative, polycythemia results from a reduction in the volume of blood plasma and is caused by loss of fluid, as from heavy perspiration or from diarrhea. Secondary polycythemia is characterized by an absolute increase in the number of erythrocytes, as with oxygen deficiency in the mountains, heart disease, or pulmonary emphysema. Secondary polycythemia accompanied by an increase in the volume of blood plasma is called polycythemia vera, or erythremia.