What Causes Deep Vein Thrombosis (DVT)?

Deep vein thrombosis (DVT) is a blood clot that forms in a vein inside a muscle. It usually happens in your legs, but you can also get them in your arms, chest, and other areas of your body.

It can be serious. It may make your leg hurt and swell. The clot might move and get stuck in a blood vessel in your lungs, brain, or heart. That could cause organ damage and even death -- within hours.

The main cause of DVT is poor blood flow. When it slows, blood can pool, which gives the cells a chance to stick together and start clotting. Someone whose blood clots easily is also at greater risk.

Surgery

You're more likely to get a clot after any surgery that reduces blood flow to a part of your body or after major surgery on your legs, belly, or chest. That includes orthopedic surgery, such as a hip replacement, and abdominal surgery where you'll be under general anesthesia for more than 30 minutes.

The procedure could set tissue, protein, and fats loose in your veins. If the wall of a vein gets accidently damaged, it can release chemicals that trigger blood clotting.

Following major surgery, you'll probably be on bed rest. You won't be using your leg muscles, and that slows your blood flow.

Medical Conditions and Treatments

DVT can happen at any age, but being older than 60 makes it more likely.

Any illness that puts you in bed for more than 3 days can set you up for DVT. And if you've had circulation or clotting problems before, you could have them again.

These are some of the most common medical risk factors for DVT:

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Your Lifestyle and Habits

When you spend a lot of time sitting or don't move much, like on a long plane flight or a long car trip, blood tends to settle in your legs.

Extra weight will put extra pressure on the veins in your lower body, which makes it harder to move the blood.

Smoking affects both circulation and clotting.

Upper-Body DVT

Although it's rare, you can get DVT in your upper body, too. A few things that can raise your chances are:

  • Having a long, thin, flexible tube (catheter) in an arm vein
  • Getting a pacemaker or implantable cardioverter defibrillator (ICD) for certain heart conditions
  • Cancer near a vein

It's very unlikely, but overworking the muscles in your arms over time might lead to a clot in them.

WebMD Medical Reference Reviewed by Jennifer Robinson, MD on January 16, 2015

Sources

SOURCES:

Society for Vascular Surgery: "Deep Vein Thrombosis (DVT)."

MedlinePlus: "Medical Encyclopedia: Deep vein thrombosis."

American Academy of Family Physicians: "Deep Vein Thrombosis: What You Should Know."

American Academy of Orthopaedic Surgeons: "Deep Vein Thrombosis."

WebMD Medical Reference from Healthwise: "Deep Vein Thrombosis - What Increases Your Risk."

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