Etiology and Risk Factors of Deep Vein Thrombosis

What are the causes of deep vein thrombosis?

Blood is meant to flow; if it becomes stagnant there is a potential for it to clot. The blood in veins is constantly forming microscopic clots that are routinely broken down by the body. If the balance of clot formation and resolution is altered, significant clotting can occur. A thrombus can form if one, or a combination of the following situations is present.

Immobility - causes blood flow in the veins to be slow. Slow-flowing blood is more likely to clot than normal-flowing blood.

• Prolonged travel and sitting, such as long airplane flights ("economy class syndrome"), car, or train travel
• Hospitalization

• Surgery
• A surgical operation that lasts more than 30 minutes is the most common cause of a DVT. The legs become still when you are under anaesthetic. Blood flow in the leg veins can become very slow.

• Trauma to the lower leg with or without surgery or casting
• Pregnancy, including 6-8 weeks post partum
• About 1 in 1,000 pregnant women have a DVT while they are pregnant, or within about six months after they give birth.
• Obesity

Hypercoagulability (coagulation of blood faster than usual)

• Medications (for example, birth control pills, estrogen)
• The contraceptive pill and hormone replacement therapy (HRT) that contain oestrogen can cause the blood to clot slightly more easily.
• Smoking
• Genetic predisposition
• Polycythemia (increased number of red blood cells)
• Cancer
• Conditions that cause the blood to clot more easily than normal (thrombophilia)
• Some conditions can cause the blood to clot more easily than usual. For example, nephrotic syndrome and antiphospholipid syndrome. Some rare inherited conditions can also cause the blood to clot more easily than normal. For example, factor V Leiden

Trauma to the vein - Damage to the inside lining of the vein increases the risk of a blood clot forming. For example, a DVT may damage the lining of the vein. So, if you have a DVT, then you have an increased risk of having another one in the future. Some conditions such as vasculitis (inflammation of the vein wall) and some drugs (for example, some chemotherapy drugs) can damage the vein and increase the risk of having a DVT.

• Fracture to the leg
• Bruised leg
• Complication of an invasive procedure of the vein