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The extra red blood cells make your blood thicker than normal. As a result, blood clots can form more easily. These clots can block blood flow through your arteries and veins, which can cause a heart attack or stroke. Thicker blood also doesn't flow as quickly to your body as normal blood.
What causes blood clots? Blood clots may form when either the flow of blood in a vein slows, damage to a vein occurs, or the blood is more clotable. Many factors can increase a personâs risk for developing a blood clot in a vein. Common risk factors for developing a blood clot include: Immobility: Hospitalization; Being paralyzed; Prolonged sitting