Deep vein thrombosis (DVT) happens when blood flow slows or stops in a deep vein — veins located in your muscles or along your bones. When blood isn’t circulating as it should, platelets and other clotting factors begin sticking together until a blood clot forms. The clot can restrict or completely obstruct blood from traveling to the heart, which leads to swelling, pain and the appearance of a bulging blood vessel in the affected area. DVTs may occur after prolonged immobility, such as during long flights or hospitalizations, or from underlying risk factors like surgery, pregnancy, certain medications or genetic conditions.
Dr. Joseph Naoum, an endovascular and vascular surgeon at Houston Methodist Cardiovascular Surgery Associates and Houston Methodist Clear Lake Hospital, uses a metaphor to explain why issues arise when platelets and clotting factors cluster together: “Imagine a main highway and its feeder roads. An accident on a feeder road would block that road, causing a bottleneck without directly affecting the main highway,” he says. “Conversely, an accident on the highway can plug up that route, cause significant congestion, and also impact traffic flowing in from the feeder roads.”
This is what happens in our body when a blood clot forms in a deep vein versus a superficial one. Unlike superficial veins (the feeder roads) that sit closer to the skin, deep veins perform the majority of the work in circulating blood back to the heart. A clot can partially or completely obstruct blood flow and affect the entire system, causing more serious complications.
Here’s what you should know about your risk, along with products that may help with prevention and recovery, according to vascular specialists.
Who is at greatest risk?
Up to 80% of DVT cases occur in people with at least one known risk factor. Having one or more risk factors also increases your risk for developing multiple DVTs in the future. Some common DVT risk factors include:
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Having a family history of blood clots or genetic conditions that increase clotting risk
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Having surgery, especially involving the lower extremities or neurovascular system
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Pregnancy or recent childbirth
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Some medications, like oral contraceptives
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Having a personal history of DVT or other blood clotting disorders
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Cancer and some of its treatments
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Antiphospholipid antibody syndrome (APLS), a rare autoimmune disorder
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Having one or more chronic health condition involving the heart, kidneys, circulatory system or lungs
Naoum says a genetic predisposition for hypercoagulable disorders, often indicated by a family history of clotting, is a strong predictor of DVT. Research shows that people with factor V Leiden mutation or prothrombin gene mutation, for example, have a significantly higher risk of developing DVT than those without these genetic variants. Other inherited clotting disorders that increase DVT risk include protein C deficiency, protein S deficiency and factor XII deficiency.
Lifestyle factors can increase your risk
While certain health conditions and medications can increase your risk of blood clots, lifestyle choices also play a significant role. “Any condition that leads to persistent or prolonged immobility can increase the risk of developing DVT,” says Naoum.
Being sedentary or sitting for long periods, especially during travel or while recovering from surgery, impacts blood flow and increases your chance of developing a blood clot. Patients in hospitals or long-term care facilities face a higher risk because their body’s natural mechanisms for preventing clots, such as regular movement and activity, are limited.
Other lifestyle factors that increase your risk include having a sedentary job, having a broken bone or a cast, being on bed rest and experiencing a trauma.
Symptoms of DVT
According to the American Academy of Orthopaedic Surgeons, many people don’t experience any symptoms of DVT. But when symptoms are present, they typically include:
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Swelling in the affected leg
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Redness or discoloration of the skin
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Veins that look larger, thicker or more swollen than usual
“Blood clots can range from 2.5 to 15 millimeters in diameter and, if left untreated, depending on the location of a clot in the leg (i.e., above the groin-iliofemoral veins or the groin-knee-femoropopliteal veins) patients can sustain chronic swelling and ulceration to their legs, known as the post-thrombotic syndrome (PTS),” says Dr. John Shao, an interventional cardiologist at Newark Beth Israel Medical Center and RWJBarnabas Health Medical Group. PTS leads to leg pain, swelling and discoloration, and may require lifelong treatment.
“A more serious consequence [of DVT] is that the blood clot can dislodge from the vessel wall and travel to the lungs, becoming a potentially life-threatening condition known as pulmonary embolism (PE),” says Shao. People with a pulmonary embolism experience sudden shortness of breath, chest pain, cough and lightheadedness. PEs can be fatal.
When to seek advanced care and treatment options
If you experience any of the symptoms mentioned or have DVT risk factors, you should see a vascular specialist for a thorough workup. Shao says that “consistent leg pain or swelling, especially with concurrent shortness of breath or chest pain,” requires immediate medical attention at a hospital or medical facility.
“An ultrasound will be performed there to confirm the blood clot’s size, location and acuity, so your doctor can decide on the proper treatment options,” Shao says. “We will also perform a CAT scan, if indicated, to rule out a pulmonary embolism, which is more dangerous.”
While treatment depends on the blood clot, the severity of your symptoms and your health, Shao says that anticoagulant medications, like intravenous heparin, injectable Lovenox and oral warfarin or direct oral anticoagulants (DOACs), are used to thin the blood and prevent blood clots from growing. Other options include a catheter-directed thrombolysis or mechanical thrombectomy procedure to remove the clot, vein stenting and compression therapy (compression stockings or devices) to improve venous return in the legs.
Reducing your risk of DVT
You can’t control all risk factors for DVT, such as inherited blood clotting disorders or a family history of clots, but you can take steps to enhance circulation. Dr. Kofi Quaye, a board-certified vascular surgeon at Cardiothoracic and Vascular Surgeons in Austin, Texas, says compression stockings aid blood flow and alleviate symptoms in people with venous insufficiency or a history of blood clots.
“We recommend compression stockings as a first form of noninvasive treatment for varicose veins,” says Quaye. According to a 2022 study in Frontiers in Cardiovascular Medicine, varicose veins (a common sign of venous insufficiency) are associated with an increased risk of venous thromboembolisms, including deep vein thrombosis and pulmonary embolism.
Quaye explains that understanding how your circulatory system works and how blood clots form can help you see the benefits of compression therapy. “Our heart works to pump oxygenated blood out to the body through high-pressure vessels called arteries, while the deoxygenated blood returns through the lower-pressure vessels called veins,” he says. These veins have structures called valves that ensure the blood flows one way from the legs to the heart. “This is also aided by contraction of muscles in the leg with walking.”
If these valves become damaged, blood accumulates in the veins until pressure increases, triggering an inflammatory process. “This inflammation, coupled with increased venous pressures, leads to the development of spider veins, varicose veins, skin changes and even ulcerations in severe forms,” says Quaye.
Compression therapy using stockings or intermittent pneumatic compression devices (IPCDs) squeeze the legs to create pressure that pushes blood back towards the heart. IPCDs, which consist of inflatable boots or sleeves placed around the legs that are periodically inflated with air, are often used in the hospital to prevent DVT in high-risk patients.
Best products for DVT prevention
The degree of a patient’s symptoms dictates the recommended compression in terms of the pressure, or millimeters of mercury (mmHG), says Quaye. Standard over-the-counter compression stockings include class 1 and some class 2, while other classes (3 and 4) often require a prescription.
Here’s a breakdown of what each class means:
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Class 1: Mild compression (8–15 mmHg) for minor leg swelling and discomfort
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Class 2: Mild to moderate compression (20–30 mmHg) for improving blood flow in people prone to swelling
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Class 3: Firm compression (30–40 mmHg) to manage more severe leg symptoms or conditions like varicose veins or lymphedema
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Class 4: Extra-firm compression (40–50 mmHg) for advanced venous insufficiency or post-thrombotic syndrome
Medical grade compression stockings
Quaye says medical-grade refers to compression of at least 20 to 30 mmHg. These are best for people with severe venous insufficiency or a history of DVT and are typically prescribed by a doctor. Your provider will tell you what length and style (such as knee-high or thigh-high stockings) based on your needs.
Medical grade compression sleeves and garments
Compression sleeves and garments offer more targeted compression to your arms or calves. Your doctor may recommend one if you have a specific injury or condition, such as lymphedema or a previous blood clot in your arm, that increases your risk of blood clots.
Non-medical grade compression socks
Light compression is ideal for everyday wear, especially if you stand or sit for long periods at work or while traveling. According to a pilot study on prenatal vascular insufficiency in the Journal of Vascular Surgery: Venous and Lymphatic Disorders, it may also help improve pregnancy-related leg swelling.
Intermittent pneumatic compression devices (IPCD)
Your doctor may recommend an intermittent pneumatic compression device if you’ve had a DVT. These devices use cuffs that wrap around your legs and inflate with air to mimic the natural muscle contractions of walking. While some IPCDs are reserved for the hospital or medical office, there are also options for home use. However, most require a valid prescription from a doctor.
Meet the experts
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Dr. Joseph Naoum, MD, endovascular and vascular surgeon at Houston Methodist Cardiovascular Surgery Associates and Houston Methodist Clear Lake Hospital
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Dr. John Shao, MD, interventional cardiologist at Newark Beth Israel Medical Center and RWJBarnabas Health Medical Group
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Dr. Kofi Quaye, MD, board-certified vascular surgeon at Cardiothoracic and Vascular Surgeons in Austin, Texas
Our health content is for informational purposes only and is not intended as professional medical advice. Consult a medical professional on questions about your health.