Phlebotomy (Bloodletting) & Erythrocytosis (thick blood): phlebotomy is the practice of bleeding a patient.
By my recount of the data, this practice is outdated and does not have much use in modern medicine, especially for managing Erythrocytosis.
It is an interesting thing that bodybuilders today still use bloodletting by the advice of their doctors because they don't know how to properly use gear.