Clinical meaning
Polycythemia means too many red blood cells. Thick blood flows slowly and can form clots, leading to stroke, heart attack, or pulmonary embolism.
Primary polycythemia (polycythemia vera, PV) is a bone marrow cancer where a JAK2 V617F mutation (>95% of cases) causes excess RBC production without normal signals. Secondary polycythemia occurs when the body produces extra RBCs in response to low oxygen — from chronic lung disease, high altitude, sleep apnea, or heavy smoking.
PV presents with a ruddy (red, flushed) complexion and itching after warm baths (aquagenic pruritus from histamine release). Treatment includes regular phlebotomy (removing blood to lower RBC count) and low-dose aspirin to prevent clots.
Exam relevance
Risk factors: - JAK2 V617F mutation (PV) - Chronic lung disease/COPD (secondary) - Chronic smoking - Obstructive sleep apnea - Living at high altitude - Dehydration (relative polycythemia) - EPO-secreting tumors - Congenital heart disease with right-to-left shunt