Being treated for polycythemia vera with phlebotomies. how does taking blood approximately every six weeks treat this condition? i don't understand.

Decr risk clotting: Keeping the hematocrit in a normal range (hct <45% in men & 42% in women) can decrease the risk of thrombosis (blood clots) in polycythemia vera (pv). Phlebotomies can reduce the hct. For patients at high risk for thrombosis (age >60 or hisotry of thrombosis) phlebotomy can be combined with Hydroxyurea to lower hct. Keeping WBC in the normal range may also be important.