Erythrocytosis is a medical condition that arises when the body produces too many red blood cells. It can lead to complications such as blood clots and strokes. It is also called polycythemia, erythrocythemia or primary polycythemia. Polycythemia vera is another name for primary polycythemia, a rare and serious condition that can cause significant health problems. Secondary erythrocytosis or secondary polycythemia, on the other hand, arises from underlying medical conditions such as lung disease, heart disease, and kidney disease. The term erythrocytosis is used interchangeably with these other terms to describe this condition. Treatment options depend on the underlying cause of the condition.