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Quick Facts

Deep Vein Thrombosis (DVT)


The Manual's Editorial Staff

Last full review/revision Oct 2019| Content last modified Oct 2019
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What is deep vein thrombosis?

Thrombosis is when a blood clot (called a thrombus) blocks a blood vessel. Deep vein thrombosis (DVT) is when a blood clot forms inside a large vein. Usually the vein is deep in your leg, but a clot may form in a vein in your pelvic area or your arm.

A blood clot is good when it helps you stop bleeding after an injury. But a blood clot that happens when you're not bleeding can be dangerous.

  • Blood clots may form in deep veins when they're not supposed to

  • Blood clots may have no symptoms, or they may cause your leg or arm to swell and hurt

  • Blood clots can break loose and travel to your lung (pulmonary embolism), which causes breathing problems and may lead to death

  • To see if you have a DVT, doctors may do an ultrasound

  • Doctors may give you medicines to help keep the clot from growing and prevent it from going to your lungs

  • If medicine doesn't work or you can't take it, your doctor may put a small filter in a vein to keep a clot that breaks loose from going to your lungs

Blood clots in deep veins are more dangerous than blood clots in shallow veins close to your skin. Blood clots in shallow veins are called superficial venous thrombosis.

Deep Veins of the Leg

Deep Veins of the Leg

What causes DVT?

The main causes of DVT include:

  • Vein injury: Your vein is injured, such as in an accident

  • Blood disorder: You have a disorder that causes increased blood clotting

  • Bed rest: The blood flow in your veins is too slow because you're on bed rest (for example, after surgery or a stroke)

  • Cast or splint: A cast or splint keeps you from moving your leg

  • Leg surgery: You had surgery on your leg, such as a hip or knee replacement

You’re more likely to get blood clots if you:

  • Have cancer

  • Have a blood clot disorder that's passed along in families

  • Take certain medicines, such as birth control pills

  • Smoke cigarettes

  • Recently gave birth or had surgery

  • Are dehydrated (too little water or other fluids in your body), especially if you’re an older adult

  • Are sitting for a long period, such as on an airplane

What are the symptoms of DVT?

Half of people with DVT have no symptoms.

If the clot is in a deep leg vein, which is the most common place, then your calf or leg may be:

  • Swollen

  • Painful

  • Red

  • Tender to the touch

  • Warm

A blood clot can break off and travel to your lung. This is a life-threatening condition called pulmonary embolism. If you have this, you may have:

  • Shortness of breath

  • Chest pain

  • A weak and dizzy feeling (from low blood pressure)

What are the complications of DVT?

There are 2 main complications of deep vein thrombosis:

A pulmonary embolism may cause:

  • Shortness of breath

  • Chest pain

  • Weakness and dizziness

  • Death

Chronic venous insufficiency keeps blood from flowing smoothly through the damaged vein. It can cause permanent swelling and discomfort to your leg or arm.

How can doctors tell if I have DVT?

Doctors look for a clot with tests such as:

  • Ultrasound

  • A blood test to measure a substance released from blood clots

How do doctors treat DVT?

Treatment usually includes:

  • Blood-thinning medicines to prevent more clotting

If blood-thinning medicines don't work or you can't take them for some reason, doctors rarely may:

  • Put a clot-blocking filter in the main vein that leads to your heart—this can help prevent pulmonary embolism

Rarely, if you have a really big clot, doctors may give you clot-dissolving medicines in your vein. However, doctors don't do this often because clot-dissolving medicine can cause life-threatening bleeding.

Being physically active doesn’t raise the risk of pulmonary embolism and won’t make a blood clot more likely to break off.

How can I prevent DVT?

You can lower the chance of getting DVT if you:

  • Put your feet up when you're sitting, bend and straighten your ankles 10 times every half hour, and walk or stretch every 2 hours—this helps blood flow and lessens swelling of your legs

  • Take any blood-thinning medicine that your doctor prescribes

  • If you’re at higher risk, wear special tight stockings (compression stockings) during the day or use air-filled leg wrappings connected to a machine that squeezes your legs from time to time (intermittent pneumatic compression).

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