Deep vein thrombosis (DVT) is the formation of a blood clot in a deep vein, most commonly in the legs or pelvis.[a] Symptoms can include pain, swelling, redness, and enlarged veins in the affected area, but some DVTs have no symptoms. The most common life-threatening concern with DVT is the potential for a clot (or multiple clots) to detach from the veins (embolize), travel through the right side of the heart, and become stuck in arteries that supply blood to the lungs. This is called pulmonary embolism (PE). Both DVT and PE are considered as part of the same overall disease process, which is called venous thromboembolism (VTE). VTE can occur as DVT only, as PE with DVT, or PE without DVT. The most frequent long-term complication is post-thrombotic syndrome, which can cause pain, swelling, a sensation of heaviness, itching, and in severe cases, ulcers. Also, recurrent VTE occurs in about 30% of those in the ten years following an initial VTE.
The mechanism of clot formation typically involves some combination of decreased blood flow rate, increased tendency to clot, and injury to the blood vessel wall. Risk factors include recent surgery, older age, active cancer, obesity, personal history and family history of VTE, trauma, injuries, lack of movement, hormonal birth control, pregnancy and the period following birth, and antiphospholipid syndrome. VTE has a strong genetic component, accounting for approximately 50 to 60% of the variability in VTE rates. Genetic factors include non-O blood type, deficiencies of antithrombin, protein C, and protein S and the mutations of factor V Leiden and prothrombin G20210A. In total, dozens of genetic risk factors have been identified.