Blood Clots and Deep Vein Thrombosis (DVT)

Blood clots can be life-threatening, especially when they form in deep veins and travel to the lungs. Learn how to recognize the signs of deep vein thrombosis (DVT), understand your risk factors, and discover steps you can take to protect your circulatory health.

Once upon a time, a writer named Margaret Wise Brown wrote "Goodnight Moon," a children's book that remains a bedtime favorite to this day. The author was just 42 when she died of a pulmonary embolism. Recovering from appendicitis surgery, Brown jokingly kicked up her legs to show the nurse how well she was doing. The movement likely dislodged a blood clot that had formed earlier, sending it to Brown’s lungs and causing the pulmonary embolism that killed her.

When you cut yourself, your blood forms a clot to staunch the bleeding. But when a clot forms inside the body, it can block blood flow and become fatal, as happened to Brown, or more recently to actress Catherine O’Hara.

How Clots Happen

Doctors refer to the three main conditions leading to blood clots as Virchow’s triad, after the great 19th century German physician Rudolf Virchow. The three components of Virchow’s triad are:

1. Damage to blood vessel walls, often caused by surgery, trauma, high blood pressure, atherosclerosis or smoking
2. Slow or poor blood flow due to heart failure, inactivity such as bed rest or sitting for long periods
3. Hypercoagulability, the tendency for blood to clot too easily, which can be due to a genetic clotting disorder, dehydration, cancer or a severe infection such as COVID-19

Doctors are on the lookout for certain lifestyle or medical conditions that make people more prone to developing blood clots, including:

• Pregnancy – during which the blood makes more clotting factor to help prevent excess bleeding during childbirth
• Obesity
• Smoking
• Trauma, which can cause internal bleeding
• Heart failure
• Bed rest or long periods of inactivity
• Plaque buildup (atherosclerosis)
• Taking birth control pills
• Diabetes
• Inflammation

Clots can occur in the legs or arms, the coronary artery in the heart, veins in the brain or intestines, and the portal vein in the liver. The three most common blood clot-related conditions are ischemic stroke, in which a clot blocks an artery in the brain; myocardial infarction (heart attack), in which a clot blocks a coronary artery; and pulmonary embolism, in which a clot blocks an artery carrying deoxygenated blood to the lungs.

DVT: Dangerous and Potentially Deadly

In pulmonary embolism, a clot blocks a pulmonary artery, preventing blood from picking up oxygen in the lungs and putting potentially fatal strain on the heart. About 90% of pulmonary embolism cases are caused by clots that form in the legs and travel to the lungs. Most often, this is due to a condition called deep vein thrombosis, or DVT.

Each year, between 60,000 and 100,000 Americans die of a pulmonary embolism from untreated DVT. While DVT can occur in various parts of the body, the clots originate most often in deep veins of the lower leg, thigh or pelvis. Pulmonary embolism is the most life-threatening risk posed by DVT, but blood clots in the legs can have other serious consequences:

• Chronic venous insufficiency is a complication of DVT in which the leg veins are damaged, causing blood to pool in the affected leg, which becomes painful and prone to swelling.
• Post-thrombotic syndrome is caused by scarring from a blood clot in a leg vein. This can lead to painful ulcers and sores on the leg.

DVT Symptoms

DVT produces symptoms in roughly half the people affected. Symptoms usually only appear in one leg and may include:

• Leg swelling
• Pain and tenderness in the calf or thigh
• Cramping in the affected leg
• Warmth in the affected area
• Skin discoloration
• A feeling of tightness in the calf

When a clot travels to the lungs, it becomes a life-threatening pulmonary embolism. Seek emergency care immediately if you experience:

• Sudden shortness of breath
• Chest pain
• Rapid heart rate
• Coughing up blood
• Dizziness or feeling faint

Treating DVT

DVT treatment depends on how long the clot has been present, its size and location, and whether a person has developed post-thrombotic syndrome. Treatment focuses on keeping a clot from enlarging, preventing it from breaking off, and reducing the chances of developing additional clots.

• Blood-thinning medications may be administered, initially via injection and then orally. Blood thinners don’t dissolve a clot directly. Instead, they prevent it from growing and allow the body to gradually break it down.
• If blood thinners are not indicated, a filter may be implanted in the inferior vena cava (IVC), the large vein that returns blood to the heart. The device can trap clots traveling from the lower body before they reach the lungs.
• Large clots can be treated through a minimally invasive cath lab procedure called DVT thrombolysis. A catheter is inserted into a vein, usually at the back of the knee, and threaded to the clot with the help of guided imaging. The catheter can be used to directly apply clot-dissolving medication. Tiny devices to broaden a narrowed vein can also be inserted through the catheter.
• If a clot has been present for months or the person suffers from post-thrombotic syndrome, interventional vascular procedures such as angioplasty or stent implantation may be necessary.

Preventing DVT

There are preventive measures you can take to maintain your circulatory health and reduce your chances of developing DVT:

• If you are under the weather and have been on bed rest, try to move as soon as possible.
• Don’t cross your legs while sitting – doing so can restrict blood flow
• Stretch your legs when traveling. Stand up and walk the length of the plane every hour or so when flying.
• On long car trips, pull over every hour or so and walk around for a few minutes to get your blood flowing.
• If you must remain in a seated position for a while, raise and lower your heels while keeping your toes on the floor and then raise your toes while keeping your heels on the floor.
• Don’t smoke.
• Manage your weight.
• Try to get at least 30 minutes of moderate physical activity every day.

After surgery, your risk of developing a clot is highest from two to 10 days post-procedure and remains elevated for about three months. Talk to your doctor about reducing your risk with leg exercises, compression stockings or blood thinners is appropriate.

This article first appeared in the March 2026 edition of the HealthPerks newsletter.