Mechanistic view of risk factors for venous thromboembolism.

Venous thromboembolism is an episodic disease with an annual incidence of 2 to 3/1000 per year that is associated with a high morbidity and mortality. Risk factors for venous thromboembolism come in many guises. They fit into an extended version of Virchow's triad and they tilt the hemostatic balance toward clot formation. This can be achieved by decreasing blood flow and lowering oxygen tension, by activating the endothelium, by activating innate or acquired immune responses, by activating blood platelets, or by increasing the number of platelets and red blood cells or modifying the concentrations of pro- and anticoagulant proteins in the blood. In this narrative review we will discuss the known common risk factors within this pathophysiological framework.