In polycythemia, the increased blood viscosity most commonly predisposes patients to which complication?

• A. Thrombosis
• B. Hypotension
• C. Anemia
• D. Bradycardia

Answer: (A)

In polycythemia, the red blood cell mass is increased, which makes the blood thicker or more viscous. This higher viscosity slows blood flow and promotes a prothrombotic state—platelets and clotting factors are more likely to interact, and sluggish flow can lead to clot formation in the vessels. Because of this, thrombotic events—such as deep vein thrombosis, pulmonary embolism, stroke, or heart attack—are the most common complications.

The other options don’t fit the physics of polycythemia. Thickened blood doesn’t typically cause hypotension; in fact, high viscosity can contribute to hypertension or vascular resistance rather than low blood pressure. Anemia is the opposite of polycythemia’s effect on red blood cells. Bradycardia isn’t driven by the viscosity change and isn’t the usual cardiovascular response to polycythemia.