Polycythemia refers to elevated number of circulating erythrocytes. Consequently, hematocrit is also raised. The risk factors of polycythemia are: - hypoxia - sleep apnea - certain tumors - chronic pulmonary disorder - smoking - chronic carbon monoxide exposure - high altitude - genetic mutations Reference: https://www.medicinenet.com/polycythemia_high_red_blood_cell_count/article.htm Image via: https://www.planetayurveda.com/library/primary-polycythemia-vera/