Deep vein thrombosis (DVT) refers to the formation of blood clots in blood vessels deep within the body. Most cases occur within the vessels of the thighs or lower legs, but they can also occur in other parts of the body. Unlike more superficial clots, DVT clots can break away from the vessel walls and travel throughout the bloodstream. These clots can pass through the heart and into the lungs, where they can cause a serious, potentially life-threatening condition known as pulmonary embolism.
Pulmonary embolism (a sudden blockage of a lung artery, usually caused by a blood clot that has traveled from the leg, though they can also come from the arm, abdomen, or pelvis) can damage the lungs and other organs and can lead to death.
DVT is not related to varicose veins, which form in more superficial vessels, and varicose veins are not a risk factor for DVT.
Deep veins are located near the bones and in the muscles, and they carry all the blood on its way back to the heart, like major rivers or waterways. The muscles squeeze them and help push through them. Superficial veins are closer the surface of the skin in the fatty layer. Blood flows more slowly through them, since they're not squeezed by muscles.
How is deep vein thrombosis diagnosed?
Diagnosing DVT must be done by a doctor, usually via special tests. DVT often comes on suddenly, and if it does, you'll need to go to the emergency room. If your primary care physician suspects DVT, they may refer you to a specialist — in some cases a vascular specialist (a doctor who focuses on correcting circulatory disorders).
Your doctor will usually start with a physical exam and then may use ultrasound to image your vessels and examine the blood flow in your legs. Diagnostic test include: venography, an imaging technique that uses dye to allow veins to appear on X-rays; blood test to look for D-dimer, a blood marker that can indicate the presence of a clot, though the test has a fairly high rate of false positives; and in some cases magnetic resonance imaging (MRI) or a computerized tomography (CT) scan.
DVT treatment options
Treatment for deep vein thrombosis is generally aimed at preventing the clot from getting bigger, preventing it from breaking away from the vessel wall, removing the clot, and/or reducing the risk of DVT recurring.
One of the most common first approaches is the use of drugs called anticoagulants. More commonly referred to as blood thinners, these can keep clots from growing larger and can also help prevent the formation of new clots. Certain blood thinners can cause excessive bleeding — an uncommon side effect that may be life threatening. Patients treated with those drugs are monitored through regular blood tests to ensure the blood is still able to effectively clot following an injury.
In an emergency, certain powerful medications called thrombolytics can be delivered intravenously or even directly into the clot. They can only be administered to patients who are hospitalized, usually in the intensive care unit.
If you cannot tolerate anticoagulants or other blood thinners, or if you are already being treated with blood thinners but still form clots, your doctor can surgically inset filters to prevent the clots from reaching the lungs, should they break away.
Many DVT sufferers are also prescribed compression stockings, tight-fitting hose that help maintain effective blood circulation in the lower legs and help keep clots from forming. You often have to use these for at least two years after DVT.
What are the symptoms of DVT?
About half of people with DVT don't have any symptoms at all until the clot breaks away. The other half have some early-warning symptoms indicating presence of a clot:
- Swelling of the affected leg or vessels of the leg
- Increased warmth in the leg
- Redness or other discoloration
- Leg pain
In the case of pulmonary embolism, the warning signs — which merit immediate medical attention — include:
- Unexplained difficulty breathing or shortness of breath
- Rapid heart rate
- Coughing up blood
- Chest pain that gets worse with deep breathing or coughing
- Lightheadedness, low blood pressure, or fainting
Who is typically affected by DVT?
Clots that lead to deep vein thrombosis tend to form because one of three things happens:
- The vein is damaged, either physically, by a chemical or radiation, or by a bodily process like an autoimmune response.
- The blood is thicker than normal. Hormonal medications (including birth control pills) can cause this, as can some hereditary disorders.
- Blood flow is slowed, usually because of reduced movement.
DVT Risk Factors
The specific factors that increase one's risk include:
- Damage to a vein from trauma (such as a fracture or a serious injury to a muscle — especially car accidents) or from major surgery (particularly anywhere from the abdomen on down)
- Slow blood flow, which can be caused by:
- Limited movement (for example, leg in a cast)
- Extended periods of sitting, like when working or traveling (and sitting with legs crossed is worse)
- Prolonged bed rest
- Increased estrogen, such as from birth control pills and certain hormone replacement therapies, which can make blood thicker and more likely to clot
- Pregnancy (up to six weeks post-birth)
- Previous history or family history of DVT
- Factor V Leiden (an inherited blood-factor condition which causes increased clotting but doesn't always lead to DVT)
- Certain diseases, such as heart disease (especially heart failure), lung disease, cancer treatment and inflammatory bowel disease (also called ulcerative colitis or Crohn’s disease)
- Placement of a central venous catheter
- Age (as you get older, your risk increases)
How can DVT be prevented?
Avoid sitting for long periods of time. Whether sitting at your desk at work, driving, or traveling as a passenger, get up and move around at least every two to three hours, making sure to exercise your legs. Wearing loose-fitting clothes when sitting helps. (It's best to avoid tight-fitting pants.) If you've been on bed rest, get up and move around as soon as possible afterwards. Try to keep to a healthy body weight. And if you believe you're at risk for DVT, talk to your doctor about compression stockings or medication.
Reviewed February 8, 2017