Venous Thromboembolism Causes and Risk Factors

What causes venous thromboembolism (VTE)?

VTE occurs in the veins that carry blood to your heart. Blood clots can develop in veins damaged by surgery or trauma, or they can develop as a result of inflammation caused by an infection or injury.

Deep vein thrombosis (DVT) may occur if the flow of blood slows down in the veins, or something damages the blood vessel lining. Pulmonary embolism (PE) refers to an embolus from a deep vein blood clot or a blood vessel in the lungs that breaks loose and travels to the lungs, blocking an artery in the lung.

Why do blood clots form?

Blood clots form naturally at sites of injury to prevent bleeding. Damage to a vein causes certain factors in the blood to trigger the activity of the enzymes thrombin. Active thrombin then forms long protein strands that clump together with platelet and red blood cells to form clots.

Learn more about how blood clots form.

What raises the likelihood of VTE?

Most often, there is more than one risk factor involved. The more risk factors you have, the greater the chance you have of developing VTE.

Not moving for long periods of time

Being still slows blood flow through the veins in your arms and legs, raising the likelihood of DVT. Especially when combined with other risk factors, DVT can develop during a long flight (more than 4 hours) or when a person is on bed rest in a nursing home, hospital setting, or after surgery. The chance of developing a blood clot is highest in the first 3 months after surgery and lowers with time. Ask your healthcare provider about prevention plans if you are scheduled for major surgery. Slower blood flow can create a low- oxygen environment that traps blood in places such as the leg veins or makes it easier for clots to form.

Learn about ways to prevent blood clots after surgery or while traveling.

Medical conditions

Certain medical conditions can raise your chance of developing VTE. Some conditions are more closely linked to developing DVT or pulmonary embolism than others and include:

Blood clotting disorders or a history of blood clots
cancer and cancer treatments including chemotherapy and surgery
Diabetes, which raises the likelihood of plaque buildup in the artery that can lead to blood clots
Heart conditions such as heart attack or congestive heart failure
High blood pressure, which can damage blood vessels
Infections, such as with SARS-CoV-2, the virus that causes COVID-19
Kidney disease, which makes the blood clot more easily
Spinal cord injury, which can damage veins deep in your body and may cause paralysis, reducing blood flow
Obesity, which can lead to inflammation and damage in the lining of blood vessels

COVID-19 is a disease caused by a virus called SARS-CoV-2. Some people with COVID-19 develop abnormal blood clots, including lots of tiny clots in the smallest blood vessels.

Age

VTE can occur at any age, but your chance goes up as you age. The chance of VTE nearly doubles every 10 years after age 40.

Family history

Your family history can affect your chances of developing VTE. Researchers have found dozens of genetic mutations (changes in the structures of your gene ) that can raise your chance of VTE. Some changes make your blood more likely to clot. If your parents have these genetic changes, you may have inherited them.

Studies show that the likelihood of VTE among the siblings of someone who has had VTE is more than double the likelihood among the general population.

Sex

Before menopause, women are more likely to get VTE compared to men. After menopause, the likelihood of VTE is higher in men.

Learn more about VTE and women.