April 18, 2011
By Harvey B. Simon, M.D.
Harvard Medical School
Last month the world was shocked to learn that tennis star Serena Williams was hospitalized with a life-threatening blood clot in her lung. This condition is called a pulmonary embolism. It was probably triggered by foot surgery followed by a long flight from New York to Los Angeles.
Although a pulmonary embolism is a blood clot in the lung, it usually starts with a clot in a leg vein. This is called a deep venous thrombosis (DVT).
One out of every 10 men will have a DVT during his lifetime. Here's what you need to know about DVTs and how to protect your veins.
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What is Deep Venous Thrombosis?
Although venous clots can sometimes form without an obvious cause, they majority of DVTs are triggered by a condition that:
- Slows the flow of blood Prolonged travel, trauma, bed rest or immobility, leg paralysis and heart failure
- Boosts the activity of the blood's clotting system Increased levels of homocysteine, an inherited or acquired clotting abnormality, various bone marrow malignacies
- Injures the wall of the vein Trauma, infection, inflammation or a previous DVT (especially common in men)
Other conditions that increase the risk of a DVT include:
- Advancing age
- Cancer that has spread throughout the body
- Certain medicines
- Cigarette smoking
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Typical symptoms include:
- Calf pain
- Calf tenderness
- Leg swelling
In most cases, only one leg is affected. The calf can feel tense and swollen, and fluid may accumulate in the ankle or foot.
In severe cases, the leg may feel warm or appear bluish; a swollen vein may also be visible. DVTs can cause fever.
Many DVTs have no symptoms. In addition, many unrelated conditions can mimic DVTs. These include:
- Muscle injuries
- Rupture of a fluid collection behind the knee
- Infection of the skin, muscles, or bones
- Accumulation of lymph fluid
So the correct diagnosis can be tricky. A high level of suspicion by the doctor and the patient is the first requirement. Without it, the doctor may not order tests to diagnose a possible DVT.
DVTs of the arm veins are relatively uncommon. Most occur when a patient in the hospital has a plastic catheter (tube) inserted in a vein to administer fluids or medication. But some are caused by unusual physical effort or by abnormal pressure on a vein from a rib.
Veins just beneath the skin can also develop clots. The vein becomes swollen, warm and tender to the touch. Because complications are rare, therapy is much simpler than for DVTs; in most cases, warm packs and nonsteroidal anti-inflammatory drugs such as aspirin or ibuprofen will do the trick.
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Getting the Right Diagnosis
Until recently, doctors thought they could diagnose a DVT by carefully examining a patient's legs. But this can miss many DVTs. Useful diagnostic tests include:
Ultrasound. A healthy vein will flutter when compressed by an ultrasound probe, but a clot-filled vein will not. Ultrasound is about 95% accurate for detecting DVTs in the large veins of the thigh. It is less accurate (about 70%) for diagnosing clots in the calf veins. That's less of a problem than it might seem. Calf vein DVTs are much less likely to break off and travel to the lungs. This makes them less dangerous.
D-dimer blood test. As the blood clotting protein fibrin breaks down, it releases smaller fragments into the bloodstream. D-dimer is one of them. It's easy to measure. A low level argues strongly against an active DVT. A high level, however, isn't nearly as helpful, because a variety of conditions can boost d-dimer levels.
Blood tests to detect over-activity of the blood clotting system. Patients with a family history of DVTs, with unusual or recurrent DVTs, or with DVTs that develop before age 45 or without evident cause are appropriate candidates for testing.
Special tests. In many medical centers helical CT has become the standard test to diagnose pulmonary emboli, the life-threatening complications of DVTs.
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Most DVTs start in the calf veins. Complications are uncommon if the clot remains in the calf; in fact, the body can often dissolve calf DVTs even without medication.
Unfortunately, though, calf vein DVTs can move up to the veins of the thigh and pelvis, which can cause major complications. These include:
- Pulmonary embolism. This is the most serious complication. It occurs when part of the clot breaks off and is carried by the blood to the lungs. Here it can block the circulation and interfere with the flow of blood. Pulmonary embolism is a medical emergency that takes up to 300,000 lives in the United States each year. Patients may develop chest pain, shortness of breath, cough, blood-tinged sputum, low blood oxygen levels, low blood pressure or abnormal heart rhythms. They can also collapse. And because many patients die before therapy can take effect, prevention is crucial.
- Permanent damage to the vein. The clot puts pressure on the vein and its valves. If the damage is severe enough, the valves are no longer able to prevent the back-flow of blood. Patients with the post-phlebetic syndrome accumulate fluid in the affected leg. This puts them at risk for infection, skin ulcers, discoloration and chronic pain.
- Recurrent DVTs. These are particularly common in men. That's why DVT patients require prolonged therapy and life-long prevention.
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The first line of treatment are medicines called anticoagulants. They are commonly referred to as "blood thinners." They prevent the blood from clotting. This stops a DVT from moving up a vein and gives the body time to dissolve the clot on its own without allowing it to break apart and move to the lungs.
Therapy has two parts:
- An injectable drug that immediately thins the blood. For years the standard drug given was heparin. It has been replaced by the low-molecular-weight heparins.
- Oral medicine for long-term treatment. Coumadin (Warfarin) has been the standard drug. But another drug called dabigatran (Pradax) is much more convenient to use. It's also much more expensive.
Therapy usually lasts for three to six months. But patients with recurrent DVTs, certain clotting abnormalities or other risk factors, or major pulmonary emboli should continue medication for a year or longer. Some patients require lifelong therapy.
The major complication of anticoagulant therapy is bleeding. In most cases, the risk can be minimized by careful therapy, but DVT patients who cannot take anticoagulants because of bleeding may need to have a filter placed in their major abdominal vein (the inferior vena cava) to protect them from pulmonary emboli.
Compression stockings can reduce the risk of permanent vein damage. The average patient can return to exercise after about a month of treatment. A few patients may benefit from "clot-busting" (thrombolytic) medications.
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Treatment may cause bleeding or other side effects. So prevention is the best treatment of all.
Many DVTs and pulmonary emboli occur in people in the hospital. Doctors can prevent these major complications by prescribing anticoagulants. In most cases, low-molecular-weight heparin is best. High-risk patients, such as those who have had hip replacements, benefit from oral anticoagulant medicines after they leave the hospital. Special leg compression stockings can protect patients who have had brain surgery and others who cannot take anticoagulants.
To prevent DVTs at home keep moving, walk nearly every day and avoid prolonged bed rest. Avoid being overweight, don't smoke and stay well-hydrated.
Any form of prolonged sitting can trigger the problem. Air travel increases the risk due to cramped quarters and dry air, which make the blood thicker and "stickier." DVTs are uncommon on flights of less than four hours, but the risk increases with longer trips, particularly those of eight hours or more. Here are some travel tips:
- Ask for a seat that gives you more leg room, such as an aisle or exit row seat.
- Don't cross your legs.
- Stretch, massage your lower legs, and pump your feet up and down for about 30 seconds every 30 minutes.
- Take a walk in the aisle at least once every hour or so.
- Drink plenty of fluids; water and juice are better than alcoholic or caffeinated beverages, which will fill your bladder nearly as much as your stomach.
- Consider breaking up very long flights into shorter segments.
- Use below-the-knee elastic support stockings during air travel. Look for a pair that applies pressure of 20 to 30 mm Hg; they are available at hospitals and large drugstores.
The risk is also higher in people who have had recent surgery, especially hip or leg operations, and in people with certain types of cancer, chronic leg swelling or heart failure. Other risk factors include obesity, smoking and any condition that results in prolonged immobility or bed rest within two weeks of the trip. People with overactive blood clotting systems and those who have had previous episodes of deep vein thrombosis face the highest risk of all.
Compression stockings gently squeeze the leg veins and make it easier for the body to keep blood flowing up to the heart. Aspirin is a very effective way to prevent clots in arteries but its value for DVTs is far less certain. An aspirin a day cant hurt, but people who need the fullest protection should ask their doctors about an injection of low-molecular-weight heparin before they take off.
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At home or in an airplane, do what it takes to protect your veins, your lungs and your life by keeping the blood moving in your legs. Be sure your doctor considers DVT prevention if you are hospitalized. Take your anticoagulant medicine if it's recommended.
Most men spend much more time thinking about SUVs than DVTs. That's okay if you're at low risk, but before you fly across the country or check into a hospital, you should show your veins the respect they deserve.
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Harvey B. Simon, M.D. is an Associate Professor of Medicine at Harvard Medical School and a member of the Health Sciences Technology Faculty at Massachusetts Institute of Technology. He is the founding editor of the Harvard Men's Health Watch newsletter and author of six consumer health books, including The Harvard Medical School Guide to Men's Health (Simon and Schuster, 2002) and The No Sweat Exercise Plan, Lose Weight, Get Healthy and Live Longer (McGraw-Hill, 2006). Dr. Simon practices at the Massachusetts General Hospital; he received the London Prize for Excellence in Teaching from Harvard and MIT.