Blood clots that form in the body can be dangerous, especially if they’re too large and become stuck in a vein. When a blood clot becomes stuck in a large, deep vein in the body, it’s called deep vein thrombosis (DVT).

According to the Cleveland Clinic, around 1 to 3 in every 1,000 American adults will develop DVT or pulmonary embolism (PE) at some point in their lives. DVT/PE are the third most common cardiovascular disease in the United States, behind heart attacks and strokes. Every year, nearly 300,000 people in the U.S. die from these conditions.¹

If left untreated, DVT can lead to other health complications in other parts of the body. Learning what the risk factors of DVT are and the signs to be aware of can help you receive the diagnosis and treatment you need quickly.

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Venous Thromboembolism: DVT and PE

When learning about DVT, it’s important to first understand the terminology used by doctors.² A venous thromboembolism (VTE) occurs when there’s a blood clot in one of your veins. There are two main types of VTE — DVT and PE.³

DVT is the most common type of VTE. It develops when a blood clot becomes stuck in deep veins, particularly in the pelvis, thigh, or lower leg. They can also develop in your arms, especially when an intravenous (IV) central line that leads to the heart is placed.

PE develops when a blood clot breaks off from another area in the body and travels through your bloodstream into your lungs. It becomes stuck in the arteries there, causing an increase in blood pressure within the lungs. Your heart also has to work harder to pump blood, which can lead to complications if left untreated. PE is common in people with DVT who have blood clots that travel from the lower part of the body up to their lungs.⁴

DVT vs. Superficial Thrombophlebitis

Another blood clotting condition that can affect your arms or legs is superficial thrombophlebitis. Also known as superficial vein thrombosis, this occurs when a blood clot develops in the superficial veins found under your skin.⁵

Superficial thrombophlebitis shares many symptoms and risk factors with DVT, but it’s a much less dangerous condition. In superficial thrombophlebitis, blood clots rarely travel to the lungs and cause a PE. It can also be diagnosed with a simple physical exam, whereas DVT requires more rigorous testing.

What Causes DVT?

Blood clots are an important part of your body’s natural healing process. When a blood vessel becomes injured, your body sends signals to your spleen to release specialized cell fragments known as platelets. These cells travel through your bloodstream and stick to the injured blood vessel, forming a plug to stop bleeding. Your body also makes proteins known as clotting factors, which help form a mesh to hold the platelet plug on the vessel. This mesh also brings in red blood cells floating by, creating a blood clot.⁶

When blood flow is slowed to the feet and legs, blood clots are more likely to develop and cause DVT. For example, DVT is common after surgery, bedrest, or sitting for too long in an airplane or car. This is why you’re encouraged to move soon after surgery or get up often during trips where you’re sitting for an extended period of time. Injuries and infections that cause inflammation can also trigger the formation of a blood clot.⁷

Risk Factors for DVT

There are numerous risk factors that increase your chances of developing DVT. Some of these can be controlled, while others can’t. Taking steps to reduce your risk of DVT can help reduce the risk of associated health complications.

Risk factors for DVT include:^1,2,8

Family history of DVT, or having a history of blood clots yourself
Increased age, particularly being over the age of 40 (though DVT can develop at any age)
Vein injuries caused by severe muscle injuries or fractures
Recovering from major surgery
Being a woman in her childbearing years (the risk decreases after menopause)
Pregnancy or recently delivering a baby
Smoking tobacco
Having certain types of cancer or undergoing chemotherapy treatments
Having an autoimmune disease such as inflammatory bowel disease, lupus, or vasculitis (inflammation of the blood vessels)
Having a blood clotting disorder, such as factor V Leiden, which causes your blood to clot very easily
Having varicose veins
Taking estrogen therapy or hormonal birth control
Being overweight or obese
Infection with coronavirus disease-19 (COVID-19)
Having a pacemaker or central venous catheter that delivers medicine to your heart

DVT Signs and Symptoms

If you notice any signs of DVT, call your doctor immediately. It’s important to begin treatment as soon as possible to lower your risk of PE and to avoid damaging your blood vessels. Signs of DVT are typically seen only in one arm or leg, rarely both. These include:¹

Pain or tenderness
Cramping or aching (common in the thigh or calf)
Warm, red, or discolored skin
Swelling
Thickening or firmness in a vein, known as a cord

Sometimes, DVT can also develop in the deep veins in your abdomen responsible for taking blood from the intestines back to the heart. This may cause nausea, vomiting, and severe stomach pain.⁹

It’s also possible that you may not experience any DVT symptoms, or you don’t notice you have a blood clot until you begin experiencing PE symptoms. These should also be treated immediately. Signs of a PE include:¹⁰

Sharp chest pain that feels similar to a heart attack; the pain may become worse with deep breathing
Shortness of breath at rest or with movement
Excessive sweating
Dizziness or lightheadedness
Fainting caused by a drop in blood pressure or heart rate, known as syncope
Fever
Fast, irregular heartbeat

How Is DVT Diagnosed?

If your doctor suspects you have DVT, they may order a few different tests to confirm a diagnosis. These include bloodwork and imaging tests to look for a blood clot in your affected arm or leg or your abdomen.

Bloodwork for DVT often includes a D-dimer test. This test measures the level of the protein fragment D-dimer that’s made when blood clots dissolve. A high D-dimer level indicates that you likely have a blood clot. However, this test alone can’t confirm DVT, so other tests must be performed.¹¹

Imaging tests are also used to take pictures of your veins to locate a blood clot. Computed tomography venography (CT venography, or CTV) is often used for diagnosing not only DVT but also PE. In CTV, an IV injection with contrast dye is inserted into a vein and an x-ray scan is taken.¹² CTV is a relatively cost-effective diagnostic method and can be performed quickly in many medical settings.

Your doctor may also perform an ultrasound, which uses sound waves that bounce off your veins and travel back into the wand (transducer) to create images. A duplex ultrasound shows how well blood is traveling through your blood vessels. They may also use a Doppler ultrasound, which provides audio to listen to your blood flow.¹³ Finally, a compression ultrasound may be done to look for blood clots in your legs. The ultrasonographer performing the test may also press the transducer onto your leg to see if your blood vessels compress or are stiff from blood clots.¹

Another imaging test used to diagnose DVT is magnetic resonance venography (MRV). Similar to magnetic resonance imaging (MRI), an MRV uses strong magnets and radio waves to create detailed images of organs and internal structures. Before an MRV, you’ll receive an IV injection with contrast dye that helps your veins stand out in the images.¹⁴

Complications from DVT

If DVT is left untreated, it can lead to blood vessel damage and chronic venous insufficiency (CVI).¹⁵ This makes it more difficult for blood in your lower legs to move back to your heart. As a result, blood begins to pool in your legs, causing an increase in pressure. CVI is also known as post-thrombotic syndrome, and it can develop in 20 to 50 percent of people who have had DVT.

The rise in pressure from CVI can cause small blood vessels known as capillaries to burst. This can cause your skin to turn a brown or red color, and it may be easily damaged if you bump into something or scratch it. You may also develop venous stasis ulcers, which are difficult to heal due to inflammation. If they become infected, it can spread to nearby tissues, resulting in cellulitis.

Preventing DVT

If you’re at an increased risk of developing DVT, you can take some steps to prevent blood clot formation. If you’re recovering from surgery or have been sitting for an extended period of time, be sure to get up and walk as much as possible. This helps move blood from your legs and feet back up to your heart. When sitting, try to avoid crossing your legs, as this can block blood flow.

If you’re taking a long trip, be sure to stay hydrated by drinking lots of water. Try to avoid alcohol or caffeine, as these pull water out of your body. If you have a layover or make a pit stop, try to walk around to keep blood from moving to your legs and feet.⁷

Making healthy lifestyle choices can also lower your risk of DVT. Avoid smoking, and maintain a healthy weight by staying active and eating a heart-healthy diet.¹