A deep venous thrombosis (DVT) results when a blood clot forms in the deep veins, often of the lower extremity. DVT may cause pain, erythema, or swelling locally but can also be asymptomatic. It carries the potential for embolization to the lungs (pulmonary embolism), which can precipitate potentially life-threatening cardiopulmonary events including cardiac arrest.

Risk factors for DVT include:

• Prolonged immobilization
• Postoperative state
• Prior history of DVT
• Pelvic / lower extremity trauma
• Older than 60
• Certain drugs: oral contraceptive pills, hormone replacement therapy, chemotherapy
• Pregnancy and postpartum period
• Presence of a central venous catheter
• Polycythemia, thrombocytosis
• Malignancy
• Chronic inflammatory diseases (eg, inflammatory bowel disease [ischemic colitis, Crohn disease], systemic lupus erythematosus)
• Hypercoagulable state (eg, antithrombin III deficiency, factor V Leiden, protein C or protein S deficiency, lupus anticoagulant, prothrombin gene mutation, anticardiolipin antibody, activated protein C resistance, hyperhomocysteinemia)
• Foam sclerotherapy (endovenous foam-induced thrombosis [EFIT])
• Endovenous laser ablation or radiofrequency ablation (endovenous heat-induced thrombosis [EHIT])

Once diagnosed, anticoagulation is initiated in efforts to stabilize the existing thrombus, prevent further thrombus aggregation, and allow for dissolution over time. Duration of therapy depends on the inciting etiology and patient substrate. Barring any contraindication to anticoagulation, treatment should be initiated urgently once the condition is diagnosed to prevent clot extension or pulmonary embolism.