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Deep Vein Thrombosis (DVT)


The Manual's Editorial Staff

Last full review/revision Jul 2021| Content last modified Jul 2021
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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.

Deep Veins of the Leg

Deep Veins of the Leg

What causes DVT?

The main causes of DVT include:

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

  • Shortness of breath

  • Chest pain

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

What are the complications of DVT?

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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