Deep vein thrombosis causes: Are you at risk of DVT?

The main cause of deep vein thrombosis (DVT) is poor blood flow. When circulation slows, blood can pool and more easily form clots - raising your DVT risk.

Deep vein thrombosis occurs when a blood clot forms in a vein deep inside a muscle in your body. It usually happens in legs, but can also develop in your arms, chest, or other areas of your body. And, although DVT is common, it can be dangerous. The blood clot can block your circulation or lodge in a blood vessel in your lungs, brain, heart or other area. The clot can cause severe organ damage and even death - within hours.

Causes of deep vein thrombosis: surgery

A DVT risk factor is anything that raises your risk of a certain health problem, such as certain types of surgery. These surgeries increase your DVT risk:

• Surgery that reduces blood flow to a part of your body
• Major surgery on a hip, knee, leg, calf, abdomen, or chest
• Orthopaedic surgery, such as hip replacement

These are some of the reasons why surgery can increase your DVT risk:

• Tissue debris, protein and fats may move into veins following surgery.
• Vein walls can become damaged, which may also release substances that promote blood clotting.
• Prolonged bed rest following surgery.

Causes of deep vein thrombosis: medical conditions or treatments

Surgery isn't the only cause of deep vein thrombosis. Certain medical conditions or treatments may also increase your DVT risk. For example, any condition that requires bed rest for more than three days increases your DVT risk. Other risk factors include:

• Cancer, risk increased further during treatment
• A previous history of deep vein thrombosis or pulmonary embolism
• An inherited condition that increases blood clotting
• Current use of hormone therapy, including that used for post-menopausal symptoms and family planning
• Pregnancy or having recently given birth
• Varicose veins, which are swollen, twisted, painful veins
• A history of heart or lung disease
• Inflammatory conditions such as rheumatoid arthritis and inflammatorybowel disease

Causes of deep vein thrombosis: lifestyle factors

Your DVT risk increases with age, especially after 60. There are lifestyle factors that can also contribute: 

• Sitting or inactivity for a long time
• Long periods of travel (plane, train, car)
• Being overweight or obese
• Smoking

Less common causes of deep vein thrombosis

Although rare, DVT can occur in the upper body. Factors that can raise your risk of developing DVT in your upper body:

• Insertion of a long, thin, flexible tube (catheter) in an arm vein
• Insertion of a pacemaker or implantable cardioverter defibrillator (ICD) for certain heart conditions
• Cancer near a vein
• Repeated vigorous activities using your arms (very rare)