What are the causes for Deep Vein Thrombosis
(Blood Clot in the Leg, DVT)?

Three factors may lead to formation of a clot inside a blood vessel:
  1. Damage to the inside of a blood vessel due to trauma or other conditions
  2. Changes in normal blood flow, including unusual turbulence, or partial or complete blockage of blood flow
  3. Hypercoagulability, a rare state in which the blood is more likely than usual to clot
Any event or condition that can lead to blood vessel damage, hypercoagulability, or change in blood flow can potentially cause deep vein thrombosis. The more common risk factors are:
  • Prolonged sitting, such as during a long plane flight or car ride
  • Prolonged bed rest or immobility, such as after injury or during illness (such as stroke)
  • Recent surgery, particularly orthopedic, gynecologic, or heart surgery
  • Recent trauma to the lower body, such as fractures of the bones of the hip, thigh, or lower leg
  • Obesity
  • Heart attack or heart failure
  • Pregnancy or recent childbirth
  • Being at very high altitude, greater than 14,000 feet
  • Use of estrogen therapy or birth control pills
  • Cancer
  • Rare inherited genetic conditions that lead to changes in certain blood clotting factors
  • Disseminated intravascular coagulation (DIC), a medical condition in which blood clotting occurs inappropriately, usually caused by overwhelming infection or organ failure
  • Certain heart or respiratory conditions
  • Advanced age
If an individual has one deep vein thrombosis, they are more likely to develop a second deep vein thrombosis.

Source: http://www.emedicinehealth.com