What Is Venous Thromboembolism? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Venous thromboembolism (VTE) is a disorder marked by blood clots that form in veins (blood vessels that carry blood toward your heart).

There are two main conditions that fall under the umbrella of VTE:

• Deep Vein Thrombosis (DVT) This refers to a clot that forms in a deep vein, typically in your legs. Less often, DVT can affect your arms.
• Pulmonary Embolism (PE) This describes a clot that breaks off from a vein and travels to your lungs, where it lodges and restricts blood flow.

Restricted blood flow due to deep vein thrombosis can cause redness, swelling, and pain near the site of a clot or multiple clots. But DVT can also occur without any obvious signs or symptoms, according to the National Heart, Lung, and Blood Institute (NHLBI).

A pulmonary embolism can happen without any previous signs of DVT — and if it substantially blocks blood flow to the lungs, it may be immediately life-threatening, according to the Cleveland Clinic.

When a vein is blocked due to VTE, it can cause damage to tissue both behind and ahead of the blockage. Tissue behind the blockage can be damaged by inflammation caused by blood pooling, while tissue ahead of the blockage is starved of the oxygen and nutrients it needs to function.

VTE is different than the kind of blood clots that typically cause a heart attack or stroke. Those clots occur in the arteries, which carry blood away from your heart to the rest of your body.

Sometimes, VTE doesn’t cause any noticeable symptoms, even as it potentially damages tissues in your body over time. But especially when deep vein thrombosis causes a serious vein blockage, the following symptoms may occur — usually in one leg at a time, according to the American Heart Association (AHA):

• Pain or tenderness in your leg (thigh or calf)
• Swelling in your leg (known as edema)
• Skin on your leg that’s warm, red, or painful to the touch

While symptoms of DVT don’t always require emergency medical attention, you should talk to your doctor as soon as possible after you notice them. You’ll most likely need treatment to reduce your risk of serious complications, such as a pulmonary embolism, according to the Cleveland Clinic.

PE is a potentially life-threatening emergency that can cause the following symptoms:

• Chest pain
• Shortness of breath
• Rapid breathing
• Fast heart rate
• Lightheadedness or loss of consciousness
• Unexplained sweating
• Coughing up blood

Symptoms of PE can occur suddenly, without warning or any knowledge of underlying VTE. Seek emergency medical attention if you experience these symptoms.

A number of factors can make it more likely that you’ll develop blood clots, which also means a higher risk of developing VTE. No single factor makes it more likely that a clot will block a vein or break off and travel to your lungs, the Cleveland Clinic notes.

The following factors can contribute to VTE:

• Major surgery (especially in the last three months)
• Severe injury or trauma
• Bone fractures
• Confinement to bed
• Limited movement (due to a cast or brace)
• Long periods of sitting
• Lack of exercise
• Cancer, plus cancer treatments and surgeries
• Older age (starting at age 40)
• Obesity
• Taking oral contraceptives (birth control)
• Hormone replacement therapy (taking estrogen)
• Pregnancy (higher risk persists for up to three months after giving birth)
• Infection (including COVID-19)
• Heart disease (including congestive heart failure)
• Blood clotting disorders (including sickle cell disease)
• Inflammatory bowel disease
• Smoking
• Family or personal history of VTE

Having more than one risk factor for VTE at the same time greatly increases the risk of VTE, according to the Centers for Disease Control and Prevention (CDC). But anyone can develop VTE, even without known risk factors.

People who are hospitalized have a much higher risk of VTE, often because they experience multiple risk factors — such as surgery or injury, infection, or confinement to bed. The AHA urges anyone who is hospitalized to ask about ways to help prevent VTE.

The risk of VTE during and following pregnancy is higher if you have other risk factors for VTE, as well as if you’re older, are having twins or other multiple births, or experience an illness or pregnancy complication such as preeclampsia, according to the AHA.

VTE is typically diagnosed based on your medical history, a physical exam, and both blood tests and imaging tests. These tests are needed before beginning treatment, since symptoms of VTE can resemble those of other health conditions, according to the CDC.

Blood Tests

The following blood tests may be used to help diagnose VTE:

• D-Dimer Test This test measures levels of a substance that is released in your blood when blood clots dissolve.
• Oxygen Level A low blood oxygen level may indicate reduced blood flow to the lungs caused by a PE.
• Genetic Tests In some cases, your doctor may want to check for inherited clotting disorders.

Imaging Tests

Certain imaging tests are also commonly used to help diagnose VTE:

• Vascular Ultrasound Often the first choice in imaging tests, this technique uses sound waves to view veins and blood flowing through them. In what’s known as a duplex ultrasound, sound waves are also bounced off your vein to directly evaluate blood flow.
• Magnetic Resonance Venography This technique uses radio waves to detect blood clots, and it requires lying in a standard magnetic resonance imaging machine. It may be more reliable than an ultrasound for certain areas of your body.
• Contrast Venography In this test, a catheter (thin tube) is threaded into your vein, where a contrast dye is released to make the vein visible on a traditional X-ray scan.
• Computed Tomography Pulmonary Angiography (CTPA) The standard test used to diagnose a PE, this technique uses multiple X-ray scans to create a detailed image of blood vessels in your lungs.
• Pulmonary Angiography The most definitive test for a PE, this technique is more invasive than CTPA. A catheter is threaded through a vein (usually starting in your groin), into your chest, where a contrast dye is released to provide images of blood vessels in your lung using an X-ray scan.

Your doctor may also order tests to rule out health conditions that could be causing symptoms similar to those of VTE.

VTE can develop and persist without any signs or symptoms, so you may not know how long you’ve had the condition at the time of diagnosis.

If your doctor prescribes anticoagulant drugs to help prevent blood clots, you’ll most likely take the drugs for a few months, according to the AHA. But if your VTE diagnosis doesn’t follow a known major risk factor like surgery, an injury, pregnancy, or a hospital stay, then you may take the drugs for a longer duration.

Once you develop VTE, there is a “high chance of recurrence” for the rest of your life, the AHA notes.

VTE is usually treated with drugs known as anticoagulants, but in certain situations, other drugs or techniques may be used. Rarely, surgery is used to remove a clot in a deep vein or in the lungs.

Anticoagulants

Also known as blood thinners, these drugs help prevent future clots and the growth of existing clots. Depending on the drug, they may be taken by injection (or intravenously in a hospital or clinic setting) or by mouth.

Intravenous and injected anticoagulants include the following:

• Heparin
• Fondaparinux (Arixtra)
• Dalteparin (Fragmin)
• Enoxaparin (Lovenox)

Oral anticoagulants include the following:

• Warfarin (Coumadin)
• Apixaban (Eliquis)
• Dabigatran (Pradaxa)
• Edoxaban (Savaysa)
• Rivaroxaban (Xarelto)

Taking anticoagulants increases the risk of bleeding, so people who take them need to be monitored for any unusual bleeding, according to the CDC.

Thrombolytics

Also known as clot busters, these drugs work by dissolving existing clots. They carry a much higher risk of bleeding than anticoagulants, so they’re generally used only in clinical care settings and for potentially life-threatening events, like a pulmonary embolism, according to the NHLBI.

Vena Cava Filter

For people who can’t take or don’t respond well to anticoagulants, a vena cava filter may be an option. This treatment involves inserting a filter in the inferior vena cava — a large vein that brings blood to your heart — to trap any clot that breaks off before it reaches your lungs.

Catheter-Assisted Removal

This technique may be used in urgent or emergency situations to remove a clot. It involves inserting a catheter (thin tube) into a blood vessel and extending it into your lung, where a tool or drug can be inserted through the tube to help break up a clot.

Thrombectomy or Embolectomy

Surgery to remove a clot is rarely recommended. This procedure is known as thrombectomy in cases of DVT, and as embolectomy for a pulmonary embolism.

Prevention of VTE

Not all risk factors for VTE can be modified. For example, you can’t control your age or genetic risk of clotting. But paying attention to lifestyle factors, especially getting regular movement and not sitting for extended periods of time, may reduce your risk of VTE.

Your doctor may also recommend specific steps to help prevent VTE, such as the following:

• Taking an anticoagulant drug
• Wearing compression stockings
• Getting out of bed soon after undergoing surgery

Since VTE often occurs during hospitalization, it’s a good idea to ask your healthcare team about a risk assessment for the condition once you’re admitted — or ahead of time if you have a planned surgery — according to the AHA.

Even though VTE is one of the most common causes of hospital-related deaths, studies have shown that appropriate measures to prevent the condition are taken in only 32 percent to 59 percent of hospitalized patients, according to Johns Hopkins Medicine.

The most dangerous health condition associated with VTE is a pulmonary embolism — a potentially life-threatening emergency in which a clot travels to the lungs and reduces or cuts off blood flow. PE is considered a form of VTE.

One possible complication of DVT is known as post-thrombotic syndrome, which typically develops in the weeks or months following DVT.

The following symptoms may occur in post-thrombotic syndrome, according to Cedars Sinai:

• Chronic pain at the site of DVT (usually your leg)
• Swelling at the DVT site
• Other leg symptoms, such as itching, tingling, cramping, or a sense of heaviness

It’s important to talk to your doctor if you experience any of these symptoms, since you may need to undergo tests to make sure you’re not experiencing a new DVT.

You’re more likely to develop post-thrombotic syndrome if you had DVT above your knee rather than below it, if you’re obese, if you’ve had more than one DVT, or if you don’t take an anticoagulant as recommended.

Treatment for post-thrombotic syndrome typically involves wearing compression stockings or another type of compression garment. That helps increase blood flow in your veins, which may help reduce symptoms.

Symptoms of post-thrombotic syndrome may also respond favorably to regular walking or other forms of exercise, elevating your legs when you’re resting, and applying an effective moisturizer or barrier cream to any irritated areas of your skin. Talk to your doctor about treatment options.

As many as 900,000 people could develop VTE each year in the United States, although the exact number unknown, according to the CDC. The agency estimates that 10 to 30 percent of people who experience VTE die within a month and that VTE claims the lives of 60,000 to 100,000 U.S. residents each year.

Johns Hopkins Medicine estimates that there are between 350,000 and 900,000 new hospitalization-related cases of VTE each year in the United States — and that there could be an additional one million cases that aren’t related to hospitalization.

The CDC estimates that one-third to half of people who develop VTE experience long-term complications (post-thrombotic syndrome), and that about one-third will develop VTE again within 10 years. But the incidence of post-thrombotic syndrome could be as high as 60 percent, according to Johns Hopkins Medicine.

The risk for VTE appears to vary widely in different countries around the world. One study found that even after adjusting for factors including age, body weight, and education level, residents of higher-income countries like the United States were 3.57 times more likely to develop VTE, compared with residents of lower-income countries.

A number of health conditions are linked to a higher risk of developing VTE, including cancer, pregnancy, obesity, certain forms of heart disease, and blood-clotting disorders.

Certain forms of cancer in particular are known to increase the risk of VTE, including cancers of the pancreas, stomach, brain, lungs, uterus, ovaries, and kidneys, according to the CDC. Elements of cancer treatment such as hospitalization, surgery, chemotherapy, and hormonal therapy may also raise the risk of VTE.

About 20 percent of VTE cases are linked to cancer, 20 percent are linked to surgery, and 20 to 50 percent don’t have an obvious cause, according to the Cleveland Clinic.

VTE is more common during pregnancy and after giving birth, because of changes that occur in the body that make clotting easier and prevent blood loss during childbirth. A pregnancy may also compress blood vessels around the pelvis and reduce blood flow to the legs, according to the CDC.

VTE and COVID-19

COVID-19 is known to increase the risk of VTE, especially in more severe cases that require hospitalization. Some of this risk may be due to the general increase in risk of VTE that hospitalization carries, but inflammation from the infection itself is also believed to play a role, according to The Ohio State Wexner Medical Center.

When researchers at Penn Medicine compared rates of VTE in people who were hospitalized for either COVID-19 or influenza, they found that the 90-day risk for VTE in influenza patients was 5.3 percent. For COVID-19 patients, the 90-day risk for VTE was 9.5 percent prior to the availability of COVID-19 vaccines and 10.9 percent after vaccines became available.

Another study found that in the first week following a COVID-19 diagnosis, the risk of a first-time VTE was 33.2 times higher than it was in people who didn’t develop COVID-19. The risk of VTE remained elevated even 27 to 49 weeks after a COVID-19 diagnosis, during which time people who’d had the viral infection were 1.8 times more likely to develop VTE.