Top causes of blood clots in the legs and how to avoid them

Don’t let a plane ride or an extended couch potato session put you at risk. Here’s what to do to keep your blood flowing.

Blood clots that form in the deep veins of the legs (deep-vein thrombosis, or DVT) can cause leg symptoms. Worse, the clots can break loose and travel through the blood to the heart and then to the lungs, causing a pulmonary embolism (PE).

More people die from PE each year in the United States than from breast cancer. What causes DVT and PE, what are the symptoms, and how can you prevent them?

Causes and triggers

After your arteries bring oxygen-rich blood to your legs, your veins send the blood back up to your heart and lungs (for more oxygen).

“If blood in the deep leg veins doesn’t move fast enough, or if you have a condition that makes you prone to blood clots, a blood clot can develop,” explains Dr. Sherry Scovell, a vascular surgeon who specializes in venous disease at Harvard-affiliated Massachusetts General Hospital.

Common blood clot triggers include

• being bedridden for long periods because of surgery or illness
• sitting for long periods — even three to four hours — in a car, plane, or train
• getting too little activity and sitting too much
• having blood pool in your legs because valves in a superficial vein don’t work properly (a varicose vein)
• taking a medication that promotes blood clotting.

Your risk for blood clots also increases with older age, a family history of DVT, a previous DVT, cancer, certain genes, COVID-19, heart failure, obesity, pregnancy, sickle cell disease, smoking, spinal cord injury, stroke, untreated varicose veins, and use of birth control pills or hormone replacement therapy.

Symptoms and risks

Be on the lookout for symptoms of two types of blood clots that can form in the legs.

A blood clot in the superficial veins. This is called a superficial venous thrombosis (SVT). “It causes redness, tenderness, or pain over varicose veins,” Dr. Scovell says. “Sometimes, an SVT can grow and become a deep-vein thrombosis.”

A blood clot in the deep leg veins. A DVT usually begins in one leg. “When you get a blockage, the blood can’t leave your leg easily. That leg can become swollen rather suddenly, and painful,” Dr. Scovell says. If your legs don’t normally get swollen, but one leg becomes swollen over a few days, that may be a sign of danger.

If part of that deep-vein clot breaks off and travels to the lungs, a PE occurs. “The clot gets stuck in blood vessels in the lung, you stop getting enough blood flow there, and that part of the lung dies. You have shortness of breath and chest pain when you take in a deep breath,” Dr. Scovell says.

Avoiding blood clots

There are apps available to help you determine your risk for getting a DVT. Dr. Scovell recommends an app called “Caprini DVT Risk,” available on iOS devices, such as an iPhone.

How can you avoid getting a clot when you’re stuck in situations that increase your risk, such as a long car ride? Keep the following tips in mind.

Stay hydrated. Avoid excessive alcohol intake, and drink lots of water.

Stretch your legs. Get up every hour or two and stretch your calves or move your ankles back and forth repeatedly. “The calf muscles act like pumps and propel blood through the veins,” Dr. Scovell says.

Move your legs while you’re lying down. Bend your knees, or point and flex your feet.

Wear compression stockings. They’ll help prevent swelling and keep blood from pooling in the legs.

Pay attention to your position. Avoid crossing your legs, and periodically change your position while seated.

Get an aisle seat when traveling. On a plane, train, or bus, sit in an aisle seat so you can easily get up and move around every few hours.

What if you have symptoms?

If you have new symptoms indicating the possibility of a DVT or a PE, and if you can’t speak immediately to your doctor or nurse, go to the emergency room. “It’s an emergency, not something to check out on Monday if it’s Friday,” Dr. Scovell says.

Treatment typically involves taking a blood thinner for several months or longer. “We also have to figure out why you got the blood clot. If we can’t find a reason, you may need to take a blood thinner for a longer time,” Dr. Scovell says. “And we don’t want you to ever get a blood clot again, so you’ll need to be proactive about avoiding future risks.”

Image: © gradyreese/Getty Images

How to Spot and Prevent Deep Vein Thrombosis

January 2017

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When the Clot Thickens

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Lots of things can cause pain and swelling in your leg. But if your symptoms stem from a blood clot deep in your leg, it can be dangerous. Blood clots can happen to anyone, anytime. But some people are at increased risk. Taking steps to reduce your chances of a blood clot forming in your veins can help you avoid potentially serious problems.

Blood clots can arise anywhere in your body. They develop when blood thickens and clumps together. When a clot forms in a vein deep in the body, it’s called deep vein thrombosis. Deep vein blood clots typically occur in the lower leg or thigh.

“Deep vein thrombosis has classic symptoms—for example swelling, pain, warmth, and redness on the leg,” says Dr. Andrei Kindzelski, an NIH blood disease expert. “But about 30–40% of cases go unnoticed, since they don’t have typical symptoms.” In fact, some people don’t realize they have a deep vein clot until it causes a more serious condition.

Deep vein clots—especially those in the thigh—can break off and travel through the bloodstream. If a clot lodges in an artery in the lungs, it can block blood flow and lead to a sometimes-deadly condition called pulmonary embolism. This disorder can damage the lungs and reduce blood oxygen levels, which can harm other organs as well.

Some people are more at risk for deep vein thrombosis than others. “Usually people who develop deep vein thrombosis have some level of thrombophilia, which means their blood clots more rapidly or easily,” Kindzelski says. Getting a blood clot is usually the first sign of this condition because it’s hard to notice otherwise. In these cases, lifestyle can contribute to a blood clot forming—if you don’t move enough, for example. Your risk is higher if you’ve recently had surgery or broken a bone, if you’re ill and in bed for a long time, or if you’re traveling for a long time (such as during long car or airplane rides).

Having other diseases or conditions can also raise your chances of a blood clot. These include a stroke, paralysis (an inability to move), chronic heart disease, high blood pressure, surgical procedure, or having been recently treated for cancer. Women who take hormone therapy pills or birth control pills, are pregnant, or within the first 6 weeks after giving birth are also at higher risk. So are those who smoke or who are older than 60. But deep vein thrombosis can happen at any age.

You can take simple steps to lower your chances for a blood clot. Exercise your lower leg muscles if you’re sitting for a long time while traveling. Get out of bed and move around as soon as you’re able after having surgery or being ill. The more active you are, the better your chance of avoiding a blood clot. Take any medicines your doctor prescribes to prevent clots after some types of surgery.

A prompt diagnosis and proper treatment can help prevent the complications of blood clots. See your doctor immediately if you have any signs or symptoms of deep vein thrombosis or pulmonary embolism (see the Wise Choices box). A physical exam and other tests can help doctors determine whether you’ve got a blood clot.

There are many ways to treat deep vein thrombosis. Therapies aim to stop the blood clot from getting bigger, prevent the clot from breaking off and moving to your lungs, or reduce your chance of having another blood clot. NIH scientists continue to research new medicines and better treatment options.

If you think you may be at risk for deep vein thrombosis, talk with your doctor.

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Signs and symptoms of deep vein thrombosis

• July 13, 2021

Deep vein thrombosis (DVT) occurs when a blood clot (thrombus) forms in one or more deep veins in your body, usually in your legs. Deep vein thrombosis can cause leg pain or swelling, but may be asymptomatic.

• Symptoms of deep vein thrombosis
• Causes of deep vein thrombosis
• Risk factors
• DVT complications
• Prevention of thrombosis

DVT may be associated with diseases that affect the blood clotting process. A blood clot in your legs can also form if you don’t move for a long time, such as after surgery or an accident. But walking extremely long distances can lead to blood clots.

Deep vein thrombosis is a serious condition because blood clots in your veins can travel through your bloodstream and get stuck in your lungs, blocking blood flow (pulmonary embolism). However, pulmonary embolism may occur without evidence of DVT.

When DVT and pulmonary embolism occur at the same time, it is called venous thromboembolism (VTE).

Symptoms

Signs and symptoms of DVT:

• Swelling of the affected leg. In rare cases, swelling appears on both legs.
• Pain in the leg. The pain often starts in the calf and may feel like spasms or soreness.
• Red or discolored skin on the leg.
• Sensation of warmth in the affected leg.

Deep vein thrombosis may occur without noticeable symptoms.

When to see a doctor

If you have signs or symptoms of DVT, see your doctor.

If you have signs or symptoms of pulmonary embolism (PE), a life-threatening complication of deep vein thrombosis, seek emergency medical attention.

Call 103

Warning signs and symptoms of pulmonary embolism include:

• Sudden shortness of breath
• Chest pain or discomfort that is aggravated by taking a deep breath or coughing.
• Feeling dizzy or dizzy or fainting
• Rapid pulse
• Fast breathing
• Cough with blood

Suspect deep vein thrombosis? Contact the professionals.

Causes

Anything that interferes with the normal flow or clotting of blood can cause blood clots.

The main causes of DVT are damage to the vein from surgery or trauma, and inflammation from infection or trauma.

Risk factors

Many factors can increase the risk of developing DVT, which include:

• Age. The risk of DVT increases at age 60, although it can occur at any age.
• Sitting for long periods of time, such as while driving or flying. When your legs remain motionless for several hours, your calf muscles do not contract. Muscle contractions promote blood circulation.
• Prolonged bed rest, such as during a long hospital stay or paralysis. Blood clots can form in the calves if the calf muscles are not used for a long time.
• Injury or surgery. Injury to the veins or surgery may increase the risk of blood clots.
• Pregnancy. Pregnancy increases pressure in the veins of the pelvis and legs. Women with an inherited bleeding disorder are at particular risk. The risk of blood clots as a result of pregnancy may remain up to six weeks after the baby is born.
• Contraceptive pills (oral contraceptives) or hormone replacement therapy. Both factors can increase the ability of the blood to clot.
• Exposure to drugs or chemicals. Certain drugs can cause blood clots. Before use, consult your doctor.
• Overweight or obese. Excess weight increases pressure in the veins of the pelvis and legs.
• Smoking. Smoking affects clotting and circulation, which may increase the risk of DVT.
• Cancer. Some forms of cancer increase blood levels of substances that cause blood clotting. Some forms of cancer treatment also increase the risk of blood clots.
• Heart failure. Increases the risk of deep vein thrombosis and pulmonary embolism. Because people with heart failure have limited heart and lung function, symptoms caused by even a small pulmonary embolism are more noticeable.
• Inflammatory bowel disease. Bowel disease such as Crohn’s disease or ulcerative colitis increases the risk of DVT.
• Personal or family history of DVT or PE. If you or someone in your family has had one or both of these, you may be at greater risk of developing DVT.
• Genetics. Some people inherit genetic risk factors or disorders, such as factor V Leiden, that make their blood clot more easily. The hereditary disease itself may not cause blood clots unless it is combined with one or more other risk factors.
• Risk factor unknown. Sometimes a blood clot in a vein can occur without an obvious underlying risk factor. This is called unprovoked VTE.

Complications

Complications of DVT may include:

• Pulmonary embolism (PE). PE is a potentially life-threatening complication associated with DVT. This happens when a blood vessel in your lung is blocked by a clot that travels to your lung from another part of your body, usually your leg.
  If you have signs and symptoms of PE, it is important to seek immediate medical attention. Sudden shortness of breath, chest pain when inhaling or coughing, rapid breathing, rapid pulse, feeling weak or faint, and coughing up blood can occur with PE.
• Post-phlebitic syndrome. Damage to a vein by a thrombus reduces blood flow to the affected areas, causing leg pain and swelling, skin discoloration, and skin ulcers.
• Complications of treatment. Complications may arise from blood thinners used to treat DVT. Bleeding is a side effect of anticoagulants. It is important to have regular blood tests while taking these medications.

Prophylaxis

Measures to prevent deep vein thrombosis include the following:

• Don’t sit still. If you have had surgery or otherwise been on bed rest, try to get back to work as soon as possible. If you are sitting for a while, do not cross your legs as this can block blood flow. If you are traveling long distances by car, stop about every hour and take a walk.
  If you are on an airplane, stand or walk from time to time. If you can’t do this, stretch your shins. Do some exercises. Try raising and lowering your heels while keeping your toes on the floor, then lift your toes while resting your heels on the floor.
• Do not smoke. Smoking increases the risk of developing DVT.
• Exercise and control your weight. Obesity is a risk factor for DVT. Regular exercise reduces the risk of blood clots, which is especially important for people who sit a lot or travel frequently.

16 Department of Vascular Surgery

Updated by experts. Last edited: July 13, 2021

symptoms, causes, treatment of thrombosis of the veins of the lower extremities, arteries (deep / superficial) – Department of Phlebology – NCC No. 2 (Central Clinical Hospital of the Russian Academy of Sciences) in Moscow

What is it?

Thrombosis is a pathological condition in which dense blood clots (thrombi) form in the vessels, slowing down or completely stopping the normal flow of blood. As a result, there may be a lack of nutrition of organs (ischemia), which in turn can lead to tissue death (necrosis, infarction) and death. There are two types of thrombosis: venous and arterial. From the names it is clear where the formation of blood clots occurs. In the first case – in the veins, in the second – in the arteries. The disease can occur in acute and chronic form. Arterial thrombosis is the most dangerous.

Main causes

There are three main factors for thrombus formation.

1. Damage to the vessel wall (as a result of trauma, surgery and malnutrition (cholesterol plaques form), infection, heavy lifting, childbirth, etc.).
2. Blood clotting disorder (tendency to increased clotting). Changes in blood clotting may occur due to metabolic disorders or hormonal imbalances.
3. Blood stasis . Occurs when a person remains motionless for a long time in one position (for example, in front of a computer, in an airplane seat or chained to a bed).

The risk group can also include people with varicose veins who are overweight, bad habits, leading a passive lifestyle, as well as people over 60 years old.

Symptoms of thrombosis

For arterial thrombosis, the following symptoms are characteristic:

• Sharp pain that occurs in one place and spreads to adjacent areas in the form of a pulsating stream
• Feeling of numbness of the extremities depending on the location of the thrombus, as a result of which they lose sensation and become cold
• Shortness of breath, irregular heartbeat, chest tightness (with blockage of the pulmonary artery)
• Dizziness, speech disorder (with blockage of cerebral arteries)

At venous thrombosis is observed:

• Increasing pain in the affected area
• Swelling and thickening of the veins at the location of the thrombus
• The color of the skin in this place becomes blue
• Swelling and bulging of superficial veins.

Disease diagnosis

When contacting a medical institution, the doctor diagnoses and prescribes treatment. Main diagnostic methods:

• Blood clotting tests
• Magnetic resonance phlebography
• Duplex/triplex scanning of lower limb arteries
• Duplex/triplex lower extremity vein scanning
• Duplex/triplex scanning of extracranial brachiocephalic arteries
• Duplex/triplex scanning of intracranial brachiocephalic arteries
• Duplex/triplex scanning of arteries and veins of the upper extremities
• Ascending phlebography with contrast agent
• Radionuclide thrombus location scan
• Thromboelastography.

Professionals to contact:

• Phlebologist
• Vascular surgeon
• Cardiologist
• Neurologist and others

Treatment

Depending on the severity of the disease, conservative and surgical treatment is possible.