Deep Vein Thrombosis Blood clots (thrombus) can form in superficial veins and in deep veins. When a clot occurs in a deep vein–typically in your legs–it’s called deep vein thrombosis. These clots require immediate medical care. 

Deep vein thrombosis is dangerous because the clots can break loose and travel through your bloodstream to your lungs where they can block blood flow (pulmonary embolism), a life-threatening condition. Deep vein thrombosis may also damage your vein and cause your leg to ache, swell and change color. 

A variety of situations and conditions can cause blood clots to form. For example, clots can form when you are inactive because you’re paralyzed or bedridden, or must sit on a long flight or car trip. Additionally, surgery or an injury can damage your blood vessels and cause a clot to form. Cancer can also cause DVT. Finally, some people have blood that simply clots too easily, a problem that may run in families. 

Symptoms and Treatment

If you have deep vein thrombosis, you may experience swelling, warmth and redness in the affected leg. You may also experience an ache or tenderness in your calf or thigh when you touch or squeeze it or when you stand or move, and pain that gets worse and lasts longer or becomes constant. 

It’s important to note that if a blood clot is small, it may not cause symptoms. In some cases, pulmonary embolism is the first sign that you have deep vein thrombosis. 

If your doctor thinks you have this condition, you’ll probably have an ultrasound test to measure the blood flow through your veins and help find any clots that might be blocking the flow. Other tests, such as a venogram, are sometimes used if the ultrasound results are unclear. A venogram is an X-ray test that takes pictures of the blood flow through your veins. 

If you have deep vein thrombosis, treatment begins right away to reduce the chance that the blood clot will grow or that a piece of the clot might break loose and flow to your lungs. 

Treatment usually includes taking blood thinners (anticoagulants) such as heparin and warfarin (Coumadin, for example). Heparin is given through an IV vein or as an injection. Warfarin is given as a pill. Typically, you’ll take blood thinners for at least 3 months to prevent existing clots from growing. 

Your doctor also may recommend that you prop up or elevate your leg when possible, take walks, and wear compression stockings. These measures may help reduce the pain and swelling. 

There are things you can do to prevent deep vein thrombosis. If you have surgery, you can take an anticoagulant medicine afterwards to prevent blood clots. Wearing compression stockings, and getting up and out of bed as soon as possible after an illness or surgery can also help. If you’re sitting for a long time, like during a long flight, exercise your legs to help blood flow.