My mom is a retired lab technician and said they had a patient at the last office where she worked who had polycythemia. She said he did very well with it, and came in about every two months to have a pint of blood drawn to help cut down on the numbers of red blood cells. As I recall, he lived a long life. I don't know what caused the erythrocytosis, but my mom said he had polycythemia, whatever its root cause may have been. He always had a high hematocrit, but she said it would drop after she drew that pint of blood.