DVT (deep vein thrombosis) is a blood clot that forms in a deep vein, usually in the leg. PE (pulmonary embolism) is what happens when part of that clot breaks free and travels to the lungs, where it can block blood flow and become life-threatening. Together, DVT and PE are known as venous thromboembolism, or VTE, and they affect up to 900,000 people in the United States each year.
How DVT and PE Are Connected
A DVT typically starts in the deep veins of the lower leg or thigh. Blood clots form when three conditions overlap: damage to the inner wall of a blood vessel, sluggish blood flow, and blood that clots more easily than normal. You don’t need all three at once, but the more that are present, the higher the risk.
The clot itself may stay put and cause local problems, or a piece can break off and ride the bloodstream up through the heart and into the pulmonary arteries. Once lodged in the lungs, it partially or fully blocks blood flow to lung tissue. A small clot may cause mild symptoms. A large one can cause sudden death. In fact, about 25% of people who have a PE experience sudden death as their very first symptom, with no warning signs beforehand. Between 60,000 and 100,000 Americans die of VTE each year.
Symptoms of DVT
DVT symptoms tend to develop gradually and stay focused on the affected leg. The most common signs include:
- Swelling in one leg, not both
- Pain or cramping that often starts in the calf and feels like a deep soreness
- Skin color changes on the leg, turning red or purple depending on your skin tone
- Warmth in the area around the clot
Some DVTs cause no symptoms at all, which is part of what makes them dangerous. A clot can silently grow large enough to send fragments to the lungs before you ever notice leg pain.
Symptoms of PE
PE symptoms come on suddenly and feel very different from DVT. They center on the chest and breathing rather than the leg:
- Sharp chest pain that worsens when you breathe deeply or move
- Sudden shortness of breath, even at rest
- Rapid breathing and fast heartbeat
- Coughing, sometimes with blood
- Pale, clammy, or bluish skin
- Dizziness or fainting
A PE is a medical emergency. If you or someone near you develops these symptoms, call 911 immediately. Minutes matter.
Who Is at Risk
Anything that slows blood flow, damages blood vessels, or makes blood clot more readily raises your risk. Some of the most common risk factors include:
Immobility. Long periods of sitting or lying down, whether from a hospital stay, a long flight, or recovery from surgery, slow blood circulation in the legs. More than a third of VTE cases diagnosed each year are linked to a recent hospitalization, and most of those clots don’t appear until after discharge.
Surgery and injury. Operations, especially on the hip or knee, and major trauma to the legs can damage blood vessel walls and trigger clotting.
Hormones and pregnancy. Birth control pills and hormone replacement therapy increase clotting risk. Pregnancy does the same by raising the levels of several clotting factors in the blood while also reducing the body’s natural clot-dissolving activity.
Cancer. About one in five VTE cases is related to cancer or its treatment. Tumors can release substances that activate the clotting system, and chemotherapy compounds the effect.
Other factors. Obesity, smoking, high blood pressure, advancing age, and a family history of blood clots all contribute. Some people carry inherited conditions that make their blood clot too easily, though they may not know it until a clot forms.
How DVT and PE Are Diagnosed
Doctors use different tools depending on whether they suspect a clot in the leg or the lungs.
For DVT, the standard test is a duplex ultrasound. It uses sound waves to visualize blood flow in the deep veins and can spot blockages or clots directly. It’s painless, takes about 30 minutes, and doesn’t involve radiation.
For PE, the primary imaging test is a CT pulmonary angiography (CTPA). A contrast dye is injected into a vein, and a CT scanner takes detailed images of the blood vessels in the lungs. This can reveal exactly where a clot is lodged and how large it is.
In both cases, doctors often start with a D-dimer blood test. D-dimer is a protein fragment released when a blood clot dissolves. A negative result makes a clot very unlikely and can rule out VTE without imaging. A positive result doesn’t confirm a clot (other conditions raise D-dimer levels too) but signals the need for imaging to find out for sure.
Treatment
The cornerstone of VTE treatment is blood thinners, also called anticoagulants. These medications don’t dissolve existing clots, but they stop the clot from growing and prevent new ones from forming. Your body’s own clot-dissolving system then gradually breaks down the existing clot over time.
Most people are now treated with direct oral anticoagulants, which are taken as pills and don’t require routine blood monitoring. Treatment typically starts with a higher dose for the first one to three weeks, then steps down to a lower maintenance dose. How long you stay on blood thinners depends on what caused the clot. A first-time clot triggered by a temporary risk factor like surgery might require three to six months of treatment. A clot with no clear cause, or a recurrence, may call for longer or even indefinite treatment.
For massive, life-threatening PEs, doctors may use clot-dissolving drugs or procedures to physically remove the clot, but these carry higher bleeding risks and are reserved for the most severe cases.
Long-Term Effects
Even after successful treatment, VTE can leave lasting consequences. About one in three people who have a VTE will experience another clot within 10 years.
A common complication of DVT is post-thrombotic syndrome, which affects 20% to 50% of people within two years of their diagnosis. The original clot damages the valves inside the vein, and those valves never fully recover. Blood pools in the affected leg instead of flowing efficiently back to the heart. Symptoms include chronic leg pain, heaviness, swelling, skin discoloration, and in severe cases, open sores called venous ulcers. Post-thrombotic syndrome is manageable but not curable, and it can significantly affect daily life.
PE can also cause long-term problems. Some people develop persistent high blood pressure in the lung arteries because old clot material never fully clears. This leads to ongoing shortness of breath and reduced exercise tolerance that may worsen over time.
Prevention
Up to 70% of blood clots associated with healthcare settings are preventable. In hospitals, prevention typically involves compression stockings, leg-squeezing devices, and blood thinners given before and after surgery.
Outside of the hospital, the most effective prevention strategies are straightforward. Move regularly during long periods of sitting, whether at a desk, on a plane, or during a road trip. Even flexing your calves or walking for a few minutes every hour helps keep blood circulating. Staying at a healthy weight, not smoking, and staying hydrated all reduce risk. If you’re on hormonal birth control or hormone therapy and have other risk factors, that’s worth discussing with your doctor, since the combination can meaningfully increase clot risk.