Deep vein thrombosis (DVT) happens when a blood clot forms in a deep vein, usually in the leg. The clot blocks blood flow, which can cause pain and swelling. The main causes come down to three things: blood flow slowing down, blood that clots too easily, or damage to the vein itself. When any of these happen, a clot can form.
What Causes Deep Vein Thrombosis?
The most common trigger is a lack of movement. When your leg muscles are still, blood pools in the veins instead of moving back to the heart. This can happen during a long flight, a car ride, or while recovering from surgery. Blood that sits still is more likely to clot.
Another major cause is injury to the vein. This can happen from a broken bone, a severe muscle strain, or even from a medical procedure like surgery or a central line placed in a large vein. The body responds to injury by sending clotting factors to the area, and sometimes that response goes too far.
Some people have blood that clots more easily than normal. This can be inherited, meaning it runs in families. It can also be acquired, such as from certain medications like birth control pills or hormone replacement therapy, or from conditions like cancer and autoimmune diseases.
Who Is at Highest Risk for DVT?
Risk increases with age, especially after 60. But younger people can get DVT too, particularly if they have other risk factors.
Hospitalization is a major risk factor. Being confined to bed, especially after surgery or a serious illness, dramatically raises the chances of developing a clot. Up to half of all DVT cases occur during or within three months of a hospital stay.
Other significant risk factors include:
- Obesity, which puts extra pressure on veins in the pelvis and legs
- Pregnancy and the six weeks after giving birth
- Smoking, which damages blood vessels and makes blood stickier
- A personal or family history of blood clots
- Heart failure, which reduces blood flow
- Inflammatory bowel disease or other chronic inflammatory conditions
- Varicose veins, which indicate weakened vein walls
Having multiple risk factors matters more than having just one. A young person on birth control who takes a long flight has a higher risk than an older person who is otherwise healthy.
What Does a DVT Feel Like?
A DVT usually affects one leg only. The most common symptoms are swelling, pain, and tenderness in the calf or thigh. The skin may look red or feel warm to the touch. The leg may feel heavy or achy.
Sometimes DVT causes no symptoms at all. This is why it can go unnoticed until a serious complication develops.
The most dangerous complication is a pulmonary embolism. This happens when part of the clot breaks off and travels to the lungs. Symptoms of a pulmonary embolism include sudden shortness of breath, chest pain that worsens with deep breathing, a rapid heart rate, and coughing up blood. This is a medical emergency that requires immediate care.
How Is DVT Diagnosed?
Doctors use a test called a duplex ultrasound to diagnose DVT. This test uses sound waves to create an image of blood flow in the veins. It is painless and does not use radiation. Ultrasound is highly accurate for detecting clots in the thigh and knee area.
If the ultrasound is unclear, a doctor may order a blood test called a D-dimer. This measures a substance in the blood that is present when a clot breaks down. A negative D-dimer test is very good at ruling out DVT. A positive test is not enough to confirm DVT on its own, because other conditions can raise D-dimer levels.
In rare cases, doctors may use a venogram, which involves injecting contrast dye into a vein and taking X-rays. This is more invasive and is usually reserved for situations where ultrasound results are unclear.
What Are the Treatment Options?
Treatment has two goals: stop the clot from growing and prevent new clots from forming. The main treatment is blood thinners, also called anticoagulants.
Common blood thinners include warfarin, heparin, and newer direct oral anticoagulants like rivaroxaban and apixaban. These medications do not dissolve the clot. They give the body time to break the clot down on its own, which usually takes weeks to months.
Treatment duration varies. Most people take blood thinners for three to six months. People with a higher risk of recurrence may need to take them longer, sometimes indefinitely. Your doctor will decide based on your specific situation.
Compression stockings are often recommended after a DVT. They help reduce swelling and can prevent a long-term complication called post-thrombotic syndrome, which causes chronic leg pain and swelling.
In more serious cases, doctors may use clot-dissolving medications called thrombolytics. These are reserved for large clots that threaten the limb or cause severe symptoms. They carry a higher risk of bleeding, so they are not used routinely.
Can DVT Be Prevented?
For people in the hospital, prevention is standard care. Doctors order blood thinners, compression devices, or both for patients at risk. These measures significantly reduce the chance of developing a clot while in bed.
For travel, the key is movement. Get up and walk every hour or two on long trips. If you cannot walk, flex and extend your ankles repeatedly. This works the calf muscles and keeps blood moving. Staying hydrated helps too.
For people with a history of DVT, prevention focuses on managing risk factors. This includes maintaining a healthy weight, staying physically active, and not smoking. If you are planning surgery or a long trip, talk to your doctor about whether you need extra protection.
What Is Post-Thrombotic Syndrome?
Post-thrombotic syndrome is a long-term complication of DVT that affects up to half of people who have had a clot. It happens when the vein is permanently damaged and cannot pump blood back to the heart efficiently.
Symptoms include chronic leg swelling, pain, skin discoloration, and in severe cases, skin ulcers. The symptoms can range from mild to disabling. Wearing compression stockings after a DVT reduces the risk of developing this condition.
There is no cure for post-thrombotic syndrome, but symptoms can be managed with compression therapy, leg elevation, and physical activity.
When Should You See a Doctor?
Seek medical attention right away if you have swelling, pain, or redness in one leg, especially if you have risk factors for DVT. Early diagnosis and treatment greatly reduce the risk of complications.
Go to an emergency room if you have sudden shortness of breath, chest pain, or coughing up blood. These could be signs of a pulmonary embolism, which can be life-threatening.
Do not wait to see if symptoms go away on their own. A DVT will not resolve without treatment, and the risk of a clot traveling to the lungs is highest in the first few days.
Frequently Asked Questions
Can a DVT go away on its own?
No, a DVT requires medical treatment with blood thinners to prevent the clot from growing or breaking off. Without treatment, the risk of a pulmonary embolism is significant.
How long does it take to recover from a DVT?
Most people feel better within a few weeks of starting treatment, but blood thinners are usually taken for three to six months. Full recovery of the vein can take longer.
Is flying really a risk for DVT?
Yes, sitting still for four hours or more slows blood flow in the legs and increases clot risk. The risk is higher on flights longer than eight hours, and it applies to car and train travel too.
Can exercise prevent DVT?
Regular physical activity improves circulation and helps maintain a healthy weight, both of which reduce risk. But exercise cannot fully protect someone who has multiple strong risk factors.
