relative erythrocytosis

Relative erythrocytosis, also known as relative polycythemia, is a condition where the concentration of red blood cells in the blood increases due to a decrease in plasma volume, rather than an actual increase in the total number of red blood cells. This can occur due to insufficient fluid intake, significant fluid loss from vomiting, diarrhea, or excessive sweating, or when fluid shifts from the bloodstream into tissues.12

Polycythemia, in general, is an abnormal increase in red blood cells and hemoglobin, leading to thicker blood and a higher risk of clots. This can be a response to increased oxygen demand, such as at high altitudes or due to lung disease, where hemoglobin cannot efficiently pick up oxygen. In contrast, polycythemia vera is an overproduction of red blood cells without a known cause. Treatment for polycythemia often involves reducing the red blood cell volume.21