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

inflammation

(IN-fluh-MAY-shun):

A reaction to injury of the body. The signs of inflammation are swelling, redness, or pain.

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

embolus

(EM-buh-luss):

A particle that breaks off from a blood clot or from a clump of vegetation, bacteria, or fungi and travels through the bloodstream. If the particle lodges in a blood vessel, it can block blood flow to organs in the body. The plural form of “embolus” is “emboli.”

from a deep vein blood clot or a blood vessel in the lungs that breaks loose and travels to the lungs, blocking an
arteries

artery

(ARR-tuh-ree):

A blood vessel that carries blood from the heart to the organs. Most arteries carry oxygenated blood. The pulmonary arteries carry deoxygenated blood away from the heart to the lungs.

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

enzyme

(EN-zime):

A protein that speeds up chemical reactions in the body.

thrombin. Active thrombin then forms long protein strands that clump together with
platelets

platelet

(PLAYT-let):

A tiny piece of a cell that helps form blood clots to slow or stop bleeding and to help wounds heal; also known as a thrombocyte.

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

oxygen

(OK-sih-jen):

A gas that is essential for humans and other animals to live. It is breathed into the lungs from the air. In the lungs, it enters the bloodstream, where red blood cells transport it to cells throughout your body.

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

Cancer

(KAN-ser):

Diseases in which cells divide more than they should. Cancer cells can spread to nearby tissues or to other parts of the body through the blood or other systems. Also known as malignancy.

** and cancer treatments including chemotherapy and surgery

• Diabetes, which raises the likelihood of
  plaque

plaque

(Plak):

A substance made up of fat, cholesterol, calcium, and other substances found in the blood. In some cardiovascular diseases, plaque builds up and hardens in arteries. Plaque buildup reduces blood flow and makes it more likely that blood clots will form in the arteries. These blood clots can partially or completely block blood flow and oxygen delivery to the heart, brain, kidneys, or legs, arms, or pelvis.

buildup in the
arteries

artery

(ARR-tuh-ree):

A blood vessel that carries blood from the heart to the organs. Most arteries carry oxygenated blood. The pulmonary arteries carry deoxygenated blood away from the heart to the lungs.

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

inflammation

(IN-fluh-MAY-shun):

A reaction to injury of the body. The signs of inflammation are swelling, redness, or pain.

and damage in the lining of 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

genetic

(jeh-NEH-tik):

Having to do with genes. Most genes are sequences of DNA that contain information for making specific proteins or molecules of RNA that perform important functions in a cell. The information in genes is passed from parents to children.

mutations (changes in the structures of your
genes

gene

(jeen):

The unit that passes heredity from parents to children. Genes are pieces of DNA and contain information for making a specific protein.

) 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.

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