Identifying Risk Factors for Venous Thromboembolism

Our understanding of risk factors associated with the development of venous thromboembolism (VTE) has increased steadily over the past 20 years. In the 1980s, the development of VTE was conceptualized in the context of the factors in Virchow's classic triad that he believed led to venous thrombosis. These factors were injury to the endothelium, alteration in blood flow (particularly stasis/immobility for venous thrombosis), and activation of blood coagulation.1 Patients who had a disease or condition that included one of these factors were considered to have a predisposing condition,2 whereas patients without any of these factors were categorized as having an idiopathic venous thrombosis. In the 1980s, the principal terms used to categorize acute venous thrombotic events were idiopathic and secondary venous thromboembolism. Gradually the term unprovoked, first coined by Kearon,3 began to be used instead of idiopathic, and provoked was used in place of secondary. More recently, provoking risk factors have been divided into temporary provoking risk factors and persisting provoking risk factors, although there is no strict definition of what constitutes a temporary or transient risk factor. Practically speaking, clear examples of transient provoking risk factors include a lower-extremity fracture, major surgery, and long-distance travel. However, the notion that a clinician can easily identify a provoking risk factor becomes less certain as the time between the possible provoking event and onset of acute VTE increases. Is surgery a provoking risk factor when an acute VTE develops 90 or 120 days after an operation? The best examples of a persisting provoking VTE risk factor are an active medical diseases such as cancer, inflammatory bowel disease, or nephrotic syndrome, and a chronic medical condition such as immobility or a prior history of VTE.Article see p 2092Accurate classification of an acute VTE as either provoked or unprovoked …