What is Deep Vein Thrombosis?
Deep Vein Thrombosis or DVT, is the formation of one or more blood clots in the body’s large veins, usually in the lower leg or calf. These clots can partially or completely block the vein, causing pain, swelling, and tenderness.
One in three women and men with DVT suffer a serious complication called pulmonary embolism(PE). This happens when part of the DVT breaks off and travels through the bloodstream, eventually blocking an artery that supplies blood to the lungs. PE is extremely serious and often causes sudden death. It is estimated that PE is the number one cause of death in hospitalized patients in the US.
Together, DVT and PE are known as venous thromboembolism, or VTE. Each year 350,000 to 600,000 Americans (half of them women) suffer from VTE, and these conditions may contribute to 100,000 deaths every year.4,5 In addition to painful leg symptoms and the risk of PE, blood clots can damage the veins in the legs, sometimes leading to chronic vein disease.
Despite the fact that blood clots in the veins are common and put you at risk for serious complications, public awareness is low. Three quarters of Americans have never heard of DVT, and 95% say their doctor has never discussed the condition with them. Of people who have heard of the disease, fewer than half know any of the common characteristics or conditions that put you at risk.
The good news is that DVT is treatable and often preventable. By learning how to recognize the symptoms of DVT and how to know if you are at risk, you can take steps to prevent a blood clot from forming and seek treatment before serious complications occur.
What are the symptoms of DVT?
DVT is often “silent” and produces no symptoms as much as half the time. Seek treatment immediately if you experience any of the following signs of DVT, as prompt treatment can prevent a potentially deadly PE:
- Swelling in one leg or along a vein in a leg or arm
- Pain or tenderness in one limb (may only appear when standing or walking)
- Warmth, redness, or discolored skin in the affected leg or arm
Unfortunately, the first sign of DVT is often a life-threatening pulmonary embolism. If you experience these symptoms of PE, call 9-1-1 immediately:
- Unexplained shortness of breath or difficulty breathing
- Sharp chest pain, especially during deep breathing
- Other symptoms:
- Rapid heartbeat, sweating, anxiety
- Dizziness, fainting, coughing up blood
Who is at risk for DVT?
Blood clots can occur in anyone at any age. However, like other forms of heart and blood vessel disease, DVT becomes more common as you age. Up to age 50, rates rise relatively slowly, but the risk of DVT doubles for each 10-year increase in age after 50.
Because of hormonal factors, women have a higher risk of DVT than men during their childbearing years. After age 50, men have about a 20% higher risk than women.7Overall, DVT is equally common in women and men.
DVT is more common in certain races: African Americans are at the greatest risk, with a 30% higher risk than whites. People of Asian or Native American backgrounds have a much lower risk, 70% less than whites.
Half of women and men who suffer DVT have one or more risk factors that set the stage for DVT, combined with a triggering event that actually causes the blood clot to form. In the other half of cases, the causes of DVT are not known.
Risk Factors for DVT
In addition to your age, race, and gender, certain characteristics and conditions put you at risk for DVT, including:
- Obesity and overweight, especially if you carry your weight around the hips
- Inherited blood clotting disorders (thrombophilia)
- Varicose veins (an early sign of vein problems)
Unique factors that can put women at risk include:
- Birth control pills (oral contraceptives) that contain estrogen and progestin increase a woman’s risk of blood clot 2 to 8 times. Because they contain more estrogen, contraceptive patches may carry an even greater risk. Progestin-only contraceptives do not appear to increase risk.
- Hormone replacement therapy (HRT) increases a woman’s risk of DVT by 2 to 4 times
- Pregnancy stresses the blood vessels because of hormonal changes and an increased volume of blood. During pregnancy and the first few months after the baby is born, the risk of DVT or PE is increased more than 4-fold. PE is the number one cause of maternal death in the US.
If you have more than one DVT risk factor you are at even greater risk. For example, a women who is obese (BMI over 30) has 2 to 3 times the normal risk of DVT, but if she also takes oral contraceptives, her risk increases to 10 times the normal risk.
While the above factors make you more likely to develop DVT, often a “trigger” event causes the blood clot to form. Common triggers include:
- Major surgery
- Trauma (especially fractures of the pelvis, hip, or leg)
- An extended period of immobility, for example:
- During a hospital stay
- In a nursing home
- During long travel – travel of 4 hours or more (flying, driving, or on bus or train) doubles your risk of blood clots for weeks after the trip18; longer travel increases risk even more19
Diagnosis & Treatment of DVT
How is DVT diagnosed?
If you have the symptoms of DVT, your doctor will perform a physical examination and ask you about your medical history to determine if you are at risk for DVT. A blood test called the D-dimer test may also be used to quickly rule out DVT. If it is likely that your symptoms are caused by DVT, your doctor will order an imaging test to confirm and locate any blood clots.
The most common test used to diagnose DVT is a Doppler ultrasound of the leg. This fast, simple, painless test uses sound waves (like those used to view the fetus during pregnancy) to produce images of the veins . This test is very accurate at diagnosing clots higher in your legs, but may miss some clots in the calves. If an ultrasound is inconclusive, your doctor may ask you to come back for a repeat test in 3 to 7 days, or you may have additional tests to get a closer look at the veins. An additional venogram test may also be necessary if your ultrasound results were normal, but your doctor still suspects you have a clot, especially in the pelvis.
Venography is rarely used, but remains the gold standard test for the diagnosis of DVT. A dye is injected into a vein in the foot, which highlights the leg veins on an X-ray image as the blood is carried back to the heart. A blood clot will appear as an area inside the leg veins where the dye did not penetrate.
If you have the symptoms of severe PE, you may be treated immediately because the risk of delaying treatment for testing is too great. For those with less severe PE symptoms, you may have tests to rule out other causes of the symptoms (such as heart problems), including a chest X-ray and ECG. If the doctor thinks PE is likely, she or he will order a CT pulmonary angiogram, which uses a dye injected into a vein to visualize blood flow to the lungs on a CT scanner.
How is DVT Treated?
The goal of DVT treatment is to prevent PE, stop the clot from growing, and prevent new clots from forming.
Blood thinning (anticoagulant) drugs are the main treatment for DVT. Blood thinners do not actually thin the blood, but make it less likely to clot, preventing existing clots from growing and new clots from forming. The most commonly used drugs are low molecular weight heparin (LMWH) or standard IV heparin. LMWH can be taken through an injection at home, but IV heparin requires that you remain in the hospital. Once your blood is thinned with LMWH or a heparin, you will begin taking warfarin for long-term blood thinning (usually taken for 3 to 12 months after you leave the hospital).
In most cases, enzymes in your blood will gradually break down the clot, allowing your body to reabsorb it. However, if you have a PE or a large DVT, you may also receive clot-busting drugs (such as tPA, which is also used to treat stroke) to speed up the breakdown of the clot.20 Clot-busting drugs carry a risk of excessive bleeding and are not usually necessary in women with smaller DVTs. More recently, doctors have begun treating some very severe blood clots by breaking them up with catheters (a long, thin tube inserted into your blood vessels through a small incision).
In less common cases, women who cannot take blood thinners, or who have had repeated DVTs or PEs even with treatment, may have a filter inserted into the vena cava, the large vein that takes blood from the body back into the heart. This filter does not prevent DVT, but it catches any blood clots that travel up from the legs, preventing them from getting to the lungs and causing a PE.
What is the prognosis of someone with DVT?
DVT rarely causes sudden death, and 96% of patients survive the initial event.21 In contrast, about 10% of patients with PE die within the first hour of symptoms, and a diagnosis of PE is often made only after death.1 Within one month about 6% of DVT patients and 12% of PE patients die.2
After the first month, death in patients with a DVT or PE is rarely related to the initial event. Instead, the main concern is the risk of repeated blood clots or vein problems. Women who suffer a DVT or PE are more likely to have another in the future.21However, there are steps you can take to risk reduce your risk of future problems:
People who suffer one blood clot event are at higher risk for another clot in the future. Up to 30% of those who have a DVT or PE will suffer another episode within 10 years, with the highest risk in the first 6 to 12 months.
For reasons that are not known, women are at lower risk for recurrent DVT than men. In one study of 826 patients (more than half were women), 9% of women compared with 31% of men had another episode of DVT within 5 years.
Recurrence is more likely if the first DVT was not caused by a one-time event such as trauma, surgery, or hormonal changes due to pregnancy, oral contraceptives, or hormone replacement therapy. Women who have ongoing factors that continue to put them at risk for DVT are more likely to have a recurrence, including those who have inherited blood clotting problems or cancer, or who are obese.1,24
If you had a PE, the recurrence is more likely to be another PE (60% of the time). If you had a DVT without a PE, 80% of the time the recurrence is another DVT.1.
Chronic Vein Disease
Along with the risk of recurrent blood clots, women who have suffered DVT or PE are at increased risk for developing Chronic Venous Insufficiency (CVI). This happens when a blood clot damages the valves or lining of the veins in the legs, preventing them from sending enough blood back to the heart. Pulled down by gravity, blood pools in the legs causing symptoms like swelling, pain, skin problems and leg ulcers.
One in 5 DVT patients develops severe CVI within 10 years, and more than half have some signs of chronic vein disease. See Chronic Vein Disease for more information on CVI.