Deep vein thrombosis, or DVT, occurs when a blood clot (also called a thrombus) forms in a large vein of the body. Clots form when blood pools, thickens and clumps together. DVT is most common in the thigh, lower leg and pelvis, though it can also occur in the arm.
By itself, DVT is not usually life-threatening. However, clotting in a large vein blocks some or all blood flow through that vein, causing blood to build up behind the clot. This can damage the vein, resulting in a chronic (long-term) condition called post-thrombotic syndrome (PTS). PTS symptoms include pain, swelling, discoloration and sores on the legs.
There is also a chance that the clot could break away from the wall of the vein and travel through the blood vessels. This can cause a life-threatening complication called pulmonary embolism (PE) in which a clot lodges in one of the main arteries of the lungs, preventing the flow of oxygenated blood to the body.
DVT isn’t always diagnosed, so experts aren’t sure how common it is. The Centers for Disease Control estimates that 1-2 people per 1,000 develop DVT each year. In people over 80, this number may be as high as one in 100.
In addition, an estimated 60,000 to 100,000 Americans die from PE each year. Most (but not all) of these cases are caused by DVT.
Causes and Risk Factors
Any factor that interferes with circulation or promotes clotting can increase a person’s risk for DVT, and many cases have multiple causes.
Inactivity is a major cause of DVT. Under normal circumstances, the contractions of the calf muscles as a person walks help circulate blood through the legs. But when a person is bedridden or sits for long periods during airline or car travel, the blood may pool in the legs, resulting in clots.
Some medical conditions and their treatments increase the risk of blood clots. Examples include:
Inherited clotting disorders (these affect about 5-8 percent of the population; learn how DNA health testing can tell you your risk for hereditary thrombophilia)
Recent trauma or surgery, especially to the lower extremities.
Women with elevated estrogen levels are at increased risk for clots. Risk factors include the use of some oral contraceptives and hormone replacement therapy. Risk is also elevated during pregnancy and for six weeks after giving birth.
It’s possible to have DVT without knowing it. In fact, doctors estimate that symptoms are present in only about half of all cases. These include:
Swelling in the ankle or foot (may be sudden)
Leg pain, especially calf cramps (may only be noticeable when standing or walking)
Patches of warm skin on the leg or foot
Enlargement of the surface veins near the affected area.
DVT symptoms usually occur on just one side of the body.
PE symptoms include:
Sudden shortness of breath
Chest pain that’s worsened by breathing deeply, moving or coughing
Light-headedness, dizziness, fainting
Coughing (some people, but not all, cough up blood)
Because of the potential for serious complications, it’s important to seek immediate medical attention if you have symptoms of DVT or PE. Call your doctor, or go to the nearest emergency room if your doctor is not available.
To diagnose DVT, a physician typically performs the following tests:
History and physical exam. Checks for outward signs of clotting as well as risk factors.
Ultrasound. This test uses reflected sound waves to create images of body structures. When DVT is suspected, the technician may perform a duplex venous ultrasound, which involves applying pressure to the veins during imaging. Ultrasound is safe, noninvasive and very effective at diagnosing clots in certain areas (especially the thigh).
Venography. Dye is injected into the leg veins, and an X-ray is taken of the blood vessels. This test is used when the suspected clot is in an area that is difficult to image with ultrasound, or when ultrasound is inconclusive.
MRI or CT. Both of these imaging tests create 3D images of body structures. They are especially useful at detecting clots in hard-to-image areas like the abdomen, pelvis and lungs.
Blood tests. Elevated levels of clot-dissolving substances in the blood can be signs of DVT or PE.
Treatment of DVT has several goals:
Stop new clots from forming (and existing clots from growing).
Prevent clot breakage and embolism.
Prevent long-term complications.
Depending on the severity of the condition and risk of complications, patients may be admitted to the hospital for treatment.
Anticoagulant medications (blood thinners) are usually the first line of treatment for DVT. These medications stop the blood from clotting, but won’t break up existing clots. Some anticoagulants are injected while others are taken by mouth. Anticoagulant therapy usually lasts 3-6 months.
Thrombolytic medications are used to break up clots in the case of PE and other life-threatening situations. A catheter is threaded into the vein, and the drug is injected directly into the area around the clot.
Vena cava filters are mesh screens that are placed into a large abdominal vein (the inferior vena cava) via a catheter to prevent clots from traveling into the lungs. They are usually used in people who can’t take anticoagulant medication for health reasons.
Graduated compression stockings apply gentle pressure to the lower leg that prevents blood pooling and clotting. They also help reduce swelling while the clot dissolves.
Angioplasty is a surgical procedure used to open damaged veins and restore healthy circulation in people with PST. A metal mesh tube called a stent may be placed in the vein to hold it open.
DVT is treatable, especially when detected early. However, PE can be quite serious, resulting in permanent lung damage and death. In fact, sudden death is the first symptom in about one-quarter of people who develop PE.
About 30-50 percent of people diagnosed with DVT will later develop post-thrombotic syndrome, and about one third will experience a recurrence of DVT within 10 years.
DVT and PE are often preventable. The following steps can help reduce your risk:
Before and after surgery, take all preventative medications as prescribed.
When traveling for four or more hours, find ways to contract your lower calf muscles. Walk around every 30 minutes, or do leg exercises in your seat. Avoid tight or restrictive clothing that may reduce circulation.
After an injury or surgery, try to get up and moving as quickly as possible. Many hospitals now prescribe physical therapy on the day after surgery.
Reduce your avoidable risk factors for DVT by quitting smoking, maintaining a healthy weight and controlling high blood pressure.
If you are at-risk for DVT, ask your doctor about preventative measures like medications and compression stockings.
“Deep Vein Thrombosis.” American Association of Orthopedic Surgeons, 2009. http://orthoinfo.aaos.org/topic.cfm?topic=a00219. Accessed May 2, 2014.
“Deep Vein Thrombosis.” Mayo Foundation for Medical Education and Research, 2013. http://www.mayoclinic.org/diseases-conditions/deep-vein-thrombosis/basics/definition/con-20031922. Accessed April 29, 2014.
“Deep Vein Thrombosis (DVT)/Pulmonary Embolism - Blood Clot Forming in a Vein: Facts.” Centers for Disease Control and Prevention, 2012. http://www.cdc.gov/ncbddd/dvt/facts.html. Accessed May 2, 2014.
“Deep Vein Thrombosis (DVT)/Pulmonary Embolism - Blood Clot Forming in a Vein: Data & Statistics.” Centers for Disease Control and Prevention, 2012. http://www.cdc.gov/ncbddd/dvt/data.html. Accessed May 2, 2014.
“What Is Deep Vein Thrombosis?” National Heart, Lung and Blood Institute, 2011. http://www.nhlbi.nih.gov/health/health-topics/topics/dvt/. Accessed May 2, 2014.
Tina is a Life Science Writer for a number of online publications, including Innerbody.com. Her expertise is in conveying complex scientific topics to diverse audiences. Tina earned her PhD in Biochemistry from the University of California, San Francisco and her BS degree in Cell Biology from U.C. Davis. In her spare time, she enjoys drawing science-related cartoons.