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Overview

Venous thromboembolism (VTE) consists of deep vein thrombosis (DVT), pulmonary embolism (PE), or both. The risk factors for VTE are a constellation of predisposing conditions which stem from the three principles of Virchow's triad: stasis of the blood flow, damage to the vascular endothelial cells, and hypercoagulability. The risk factors for VTE can be categorized as temporary, modifiable and non-modifiable. Venous thrombosis also shares risk factors with cardiac thrombosis, such as obesity, hypertension and smoking.

Risk Factors

Shown below is a list of predisposing factors to VTE.

Strong risk factors	Moderate risk factors	Weak risk factors
❑ Bone fracture (hip or leg) ❑ Hip replacement surgery ❑ Knee replacement surgery ❑ Major general surgery ❑ Significant trauma ❑ Spinal cord injury	❑ Athroscopic knee surgery ❑ Central venous lines ❑ Chemotherapy ❑ Chronic heart failure ❑ Respiratory failure ❑ Hormone replacement therapy ❑ Cancer ❑ Oral contraceptive pills ❑ Stroke ❑ Pregnancy ❑ Postpartum ❑ Prior history of VTE ❑ Thrombophilia	❑ Bed rest for more than 3 days ❑ Prolonged car or air travel ❑ Advanced age ❑ Laparoscopic surgery ❑ Prepartum ❑ Obesity ❑ Varicose veins

Genetic Thrombophilia

• Factor V Leiden
• Prothrombin G20210A mutation
• Protein C deficiency
• protein S deficiency
• Antithrombin deficiency
• APC resistance
• Antithrombin III deficiency
• Factor VIII mutation
• Familial dysfibrinogemia
• Hyperhomocysteinemia

Acquired Thrombophilia

• Antiphospholipid syndrome
• Heparin induced thrombocytopenia
• Nephrotic syndrome
• Paroxysmal nocturnal hemoglobinuria

Modifiable Risk Factors

Modifiable risk factors are reversible based upon lifestyle/behavior modification.

• Obesity: Obesity is defined as a body-mass index (BMI) above 30 kg/m2.
  • Within obesity, a number of additional behaviors can further contribute to an increased risk of VTE including:
    • Smoking
    • Use of oral contraceptives
    • Prolonged air travel: However, travel by air increases the risk to the same extent as travel by bus, train or car, suggesting that the increased risk of air travel is due primarily to prolonged immobility.
• Homocysteine: Elevated homocysteine has been reported as a risk factor for venous thrombosis and levels can be reduced with B vitamin supplementation.
• Smoking: Significantly increases the risk of DVT, particularly in women who are taking oral contraceptive pills.

Non-Modifiable Risk Factors

• Advanced age
• Heart failure
• Thrombophilia or hypercoagulable state
• Polycythemia vera

Temporary Risk Factors

• Injury to a deep vein from surgery, a fracture, or other trauma, especially a paralytic spinal cord injury
• Prolonged Immobilization causes stasis in the deep veins which may occur after surgery, with prolonged bedrest, or prolonged seating during travel.
• Pregnancy and the peri-partum period
• Active cancer
• Central venous catheter