Venous thromboembolism is a serious condition where blood clots form inside the veins and block the normal flow of blood through the body. Understanding this condition, its warning signs, and how to prevent it can save lives and protect your long-term health.
Understanding Venous Thromboembolism
Venous thromboembolism, often shortened to VTE, describes a condition that happens when blood clots develop within the body’s veins. The term “thrombo” refers to a blood clot, while “embolism” means a traveling particle that creates a blockage. When healthcare providers discuss VTE, they are typically talking about two closely related problems that can affect different parts of the body.[1][2]
The first type is deep vein thrombosis, or DVT, which occurs when a blood clot forms deep inside a vein, most commonly in the lower leg, thigh, or pelvis. These clots can also develop in the arms, particularly if someone has a large intravenous line inserted into a vein. The second type is pulmonary embolism, or PE, which happens when a piece of a blood clot breaks away from where it formed and travels through the bloodstream until it reaches the lungs. Once there, it can block a blood vessel, creating a life-threatening emergency.[1][3]
Blood clotting is actually a natural and healthy response when you get a cut or wound on the outside of your body. Your blood partially solidifies to keep it from leaking too quickly, forming a scab on your skin. Inside your body, the same process creates a clot. Blood clotting can also be triggered when an infection irritates the lining of a blood vessel, much like a wound would. Normally, when the wound or infection begins to heal, the clot dissolves and disappears. However, sometimes the clot fails to dissolve properly. Other times, blood clots form even when there was no injury at all. Many different factors can contribute to this abnormal clotting.[2]
The relationship between DVT and PE is particularly important to understand. About 40% of patients who have a blood clot in their deep leg veins also have an associated pulmonary embolism, even if they don’t feel symptoms from it. Going the other direction, roughly 70% of patients who experience a pulmonary embolism also have deep vein thrombosis somewhere in their body.[14]
How Common Is Venous Thromboembolism
Venous thromboembolism is remarkably common throughout the United States and around the world. In the United States alone, as many as 600,000 VTE events occur each year. The condition ranks as the third most common vascular diagnosis after heart attacks and strokes, making it one of the leading cardiovascular threats to public health.[1][2]
The annual incidence is estimated to be one or two cases per 1,000 people in the general population. Between 60,000 and 100,000 people die from VTE each year in the United States. These numbers reflect not just the frequency of the condition but also its serious nature when it goes unrecognized or untreated.[3]
When looking at how VTE presents itself, approximately one-third of patients experience pulmonary embolism, while two-thirds present with deep vein thrombosis. Pulmonary embolism tends to be more dangerous than DVT alone, carrying a higher risk of death, a greater likelihood of the clot returning, and more serious long-term complications.[14]
The impact of VTE extends beyond the immediate threat. One-half of people who develop DVT will experience long-term complications, including a condition called post-thrombotic syndrome and venous ulcers. Additionally, about one-third of patients who have a venous thromboembolism will experience a recurrence within 10 years, meaning the clotting problem can return even after successful initial treatment.[3]
Age plays a significant role in VTE risk. The chances of developing this condition increase as people get older, with the risk becoming particularly elevated after age 40 and continuing to rise with advancing age. The condition does not discriminate by gender in terms of overall frequency, although certain risk factors may affect men and women differently depending on their life circumstances.[5][7]
What Causes Venous Thromboembolism
The underlying cause of most venous thromboembolism cases is a blood clot that forms somewhere in the body’s deep veins. In the vast majority of cases, the clot starts in a deep vein of the leg and then travels through the bloodstream to reach the lungs. Less commonly, the clot may originate in the deep veins of the arms or other parts of the body.[5]
While blood clots are the most common cause, pulmonary embolism can occasionally result from other substances blocking the lung arteries. In rare situations, air bubbles, clumps of fat from a broken bone, or even pieces of tumor tissue can travel through the bloodstream and create a blockage in the lungs.[5][6]
Approximately 90% of venous gas embolism cases are iatrogenic, meaning they occur as an unintended consequence of medical or surgical procedures. These can happen during central venous line placement, head and neck surgery, chest trauma procedures, thoracentesis, hemodialysis, or when patients are on high-pressure mechanical ventilation. However, these gas embolisms represent a specific subset of VTE that differs from the more common blood clot variety.[11]
The risk of developing VTE is highest after major surgery, significant injury, or during periods of serious infection and inflammation. Surgery and injury can directly damage the veins, creating conditions where clots are more likely to form. Inflammation and infection increase the likelihood of blood clotting throughout the body as part of the immune response. Lack of movement after surgery or during recovery from an injury also contributes to clot formation because blood flow slows when muscles aren’t contracting to push blood back toward the heart.[1]
Risk Factors for Venous Thromboembolism
While almost anyone can develop venous thromboembolism, certain factors significantly increase the chances of experiencing this condition. Understanding these risk factors helps people recognize when they might be at higher risk and take appropriate preventive measures.
Having a personal history of blood clots or pulmonary embolism dramatically increases the risk of another event. Similarly, a family history of blood clots suggests there may be genetic factors at play that make clotting more likely. Certain inherited clotting disorders can run in families, and people with these conditions may need to be especially vigilant about prevention.[3][5]
Several medical conditions raise the risk of VTE. Heart disease, including heart failure, increases clotting risk. Cancer and cancer treatments are strongly associated with venous thromboembolism. Clotting disorders specifically affect how blood coagulates in the body. Even recent COVID-19 infection has been identified as a risk factor for developing blood clots.[5]
Recent surgery represents one of the highest-risk situations for VTE development, particularly joint replacement surgery and other major operations. The combination of tissue trauma, inflammation, and reduced mobility during recovery creates ideal conditions for clots to form. A broken hip or leg bone also carries substantial risk for the same reasons.[3][5]
Prolonged immobilization or bedrest significantly increases VTE risk. When muscles don’t contract regularly to help pump blood back toward the heart, blood flow slows in the veins, allowing clots to form more easily. This is why long plane flights or extended car trips can be problematic, especially journeys lasting more than three hours. Hospital stays where patients cannot move around freely also create this risk.[5][7]
Being over 60 years old increases the baseline risk for VTE. Obesity or being overweight adds to this risk because excess body weight can affect blood flow and increase inflammation throughout the body. Smoking damages blood vessels and affects clotting factors in the blood, making it another significant risk factor.[5][7]
For women specifically, pregnancy and the postpartum period carry elevated risk, with the danger remaining highest for up to six weeks after delivery but potentially lasting up to three months. Hormone-based medications such as birth control pills and hormone replacement therapy increase clotting risk because they contain estrogen, which affects blood clotting factors. Having varicose veins also contributes to higher risk because these damaged veins don’t move blood as efficiently.[3][5][7]
Having an indwelling intravenous catheter, such as a central line, creates a risk both from the presence of a foreign object in the vein and from the potential for the catheter to damage the vein wall. Severe trauma from accidents or injuries, recent hospitalization, and dehydration all add to the cumulative risk of developing venous thromboembolism.[5][7]
Sometimes, venous thromboembolism occurs without any obvious reason. When this happens, doctors may conduct additional testing to look for hidden risk factors or underlying conditions that weren’t previously known.[7]
Recognizing the Symptoms
The symptoms of venous thromboembolism differ depending on whether the blood clot is lodged in a deep vein or has traveled to the lungs. Recognizing these symptoms quickly is crucial because early treatment can prevent serious complications and save lives.
Deep Vein Thrombosis Symptoms
One particularly challenging aspect of deep vein thrombosis is that about half of people who have it experience no symptoms at all. This means many cases go undetected until complications develop or the clot is discovered during testing for another reason.[3]
When symptoms of DVT do appear, they typically occur in the affected leg or arm. Swelling is one of the most common signs, where the limb becomes noticeably larger than the other side. Pain or tenderness may develop, often described as a throbbing sensation in the calf or thigh when walking or standing. The skin around the affected area may feel warm to the touch, distinctly warmer than the surrounding skin or the same area on the other limb. Redness or darkening of the skin may appear over the painful area, though this can be harder to notice on brown or black skin.[3][7]
The veins themselves may become swollen, hard, or tender when touched. All of these symptoms can occur in the leg or arm, though leg DVT is far more common. In rare cases, symptoms may appear in the belly area if that’s where the blood clot has formed.[7]
Pulmonary Embolism Symptoms
The symptoms of pulmonary embolism can vary greatly depending on how much of the lung is affected by the blockage, the size of the clots involved, and whether the person has underlying lung or heart disease. It’s also possible to have a pulmonary embolism without having any noticeable symptoms of deep vein thrombosis first.[3][4]
Shortness of breath is one of the most common symptoms of PE. This symptom typically appears suddenly, can occur even when resting, and becomes worse with any physical activity. The person may struggle to catch their breath or feel like they can’t get enough air no matter how hard they try to breathe.[3][4]
Chest pain or discomfort is another hallmark symptom of pulmonary embolism. People often describe it as feeling like they’re having a heart attack. The pain is frequently sharp and becomes much worse when taking a deep breath or when coughing. This pain can be severe enough to prevent a person from breathing deeply.[3][4]
A rapid heartbeat or irregular heart rhythm may develop as the heart struggles to compensate for the blocked blood flow in the lungs. Similarly, rapid breathing occurs as the body tries to get more oxygen. Some people experience a cough, which may produce bloody sputum in some cases.[3]
Very low blood pressure can occur with larger clots or multiple clots, creating a dangerous situation where the body’s organs don’t receive adequate blood flow. This may lead to lightheadedness, dizziness, or even fainting.[3][5]
Sometimes people with pulmonary embolism don’t experience any symptoms until they develop serious complications such as pulmonary hypertension, which is high blood pressure in the arteries leading to the lungs. This makes early detection challenging but underscores the importance of knowing your risk factors and seeking medical attention when something doesn’t feel right.[5]
Preventing Venous Thromboembolism
Preventing blood clots is far better than treating them after they form. If you’re preparing for surgery or hospitalization, or if you have other risk factors for VTE, talking with your healthcare provider about a prevention plan is essential.
One of the most effective preventive measures is staying active. Helping your blood circulate makes it much harder for clots to form. After surgery, your healthcare provider may encourage you to start moving around as soon as possible. Even small movements matter—if you can’t get up and walk, try flexing and stretching your feet to improve blood flow in your calves. During long journeys, whether by plane, train, or car, it’s important to move about and walk around at least once every hour or two.[7][18]
Applying gentle pressure to the legs can keep blood from pooling and clotting. Your healthcare provider may recommend wearing compression stockings, which apply more pressure around the ankles and feet to encourage blood flow back toward the heart. Some hospitals use special sleeves or boots that periodically fill with air to provide rhythmic compression. These devices mimic the natural pumping action that occurs when you walk.[18]
Blood thinner medications, called anticoagulants, may be prescribed before or after surgery to prevent clot formation. Common options include heparin, which can be given as an injection, and oral medications such as direct oral anticoagulants or warfarin. Sometimes this preventive therapy starts before surgery; other times, your provider may prescribe a blood thinner to take during your recovery period at home.[18]
Maintaining a healthy weight reduces your overall risk of VTE. Regular exercise, even moderate activities like walking, helps keep blood flowing properly through your veins. If you’re a smoker, quitting tobacco is one of the most important steps you can take to lower your risk. Staying well-hydrated is also important because dehydration can make blood more likely to clot.[7]
During travel, especially trips lasting three hours or more, take several precautions. Wear loose, comfortable clothing rather than tight garments that might restrict blood flow. Drink plenty of water and avoid excessive alcohol consumption. Walk around whenever possible—on a plane, move through the cabin periodically; in a car, stop regularly to stretch your legs and walk a bit. While seated, avoid crossing your legs, as this position can affect circulation. Instead, try moving your toes up and down and rotating your ankles in circles to keep blood moving.[7][18]
If you’re going into the hospital, your healthcare team should assess your risk for developing DVT. If they determine you’re at higher risk, they may provide preventive treatment such as medication or compression stockings while you’re hospitalized. This prevention may continue even after you leave the hospital because a blood clot can develop weeks later.[7]
Understanding your personal and family history of blood clots is valuable information to share with your healthcare providers. If blood clots run in your family, genetic testing might reveal inherited clotting disorders that require special monitoring or preventive treatment throughout your life. Knowing these risks allows you and your doctors to make informed decisions about prevention strategies.[5]
How the Body Changes with Venous Thromboembolism
Understanding what happens inside the body when venous thromboembolism occurs helps explain why this condition is so serious and why treatment needs to be prompt.
Veins are blood vessels that carry blood from the outer parts of your body back to your heart. Unlike arteries, which have thick, muscular walls that help push blood forward, veins rely heavily on muscle contractions and one-way valves to move blood against gravity, especially from the legs. When a vein becomes blocked by a clot, blood starts to pool behind the blockage. This pooling causes inflammation in the vein and surrounding tissues. Meanwhile, cells located ahead of the blockage can’t receive the oxygen and nutrients they need to function properly.[2]
In deep vein thrombosis, when the blockage is significant, the backup of blood causes visible swelling in the affected limb. The inflammation in the vein wall and surrounding tissue creates pain, warmth, and redness. Over time, this inflammation can cause long-term damage to the vein itself and to the delicate one-way valves inside the vein that normally prevent blood from flowing backward. This damage can result in chronic venous insufficiency, also called post-thrombotic syndrome, where the leg continues to have problems with swelling, pain, and skin changes even after the clot is treated.[2][3]
The most dangerous complication occurs when part or all of a blood clot breaks free from where it formed. This loose piece travels through larger and larger veins as it makes its way back toward the heart. The clot passes through the right side of the heart and enters the pulmonary arteries, which carry blood to the lungs to pick up oxygen. In the lungs, the blood vessels branch into progressively smaller vessels until they become tiny capillaries where oxygen exchange takes place. When the traveling clot reaches a vessel too narrow for it to pass through, it gets stuck, creating a blockage called a pulmonary embolism.[2][4]
This blockage in the lung has several serious effects. First, the affected portion of the lung cannot perform its normal job of adding oxygen to the blood. This means the body’s oxygen levels drop, which is why shortness of breath is such a prominent symptom. Second, the blockage increases resistance to blood flow in the pulmonary arteries, forcing the right side of the heart to work much harder to push blood through. This increased resistance causes pulmonary hypertension—high blood pressure in the arteries of the lungs.[2][4]
When the right ventricle of the heart must suddenly work against this increased resistance, it can fail. Large blood clots or multiple smaller clots can create an “air lock” effect that severely impairs the right ventricle’s ability to pump blood effectively. This acute right ventricular failure can lead to cardiovascular collapse and death if not treated immediately.[2]
The severity of complications depends largely on how much of the lung’s blood flow is blocked. A small clot blocking a small vessel may cause minimal symptoms and might even resolve on its own with proper treatment. A large clot blocking a major vessel, or many smaller clots blocking multiple vessels, creates a life-threatening emergency requiring immediate intervention.[4]
If someone survives a large pulmonary embolism, they may develop long-term complications. Chronic thromboembolic pulmonary hypertension can occur when scar tissue forms in the pulmonary arteries at the site of the clot, permanently affecting blood flow to portions of the lung. This condition causes ongoing breathing problems and can be fatal if severe.[3]
Blood clots that form in smaller, more superficial veins close to the skin surface don’t typically cause the same serious complications as deep vein thrombosis. These superficial clots rarely break off and travel to the lungs, and they generally don’t cause long-term damage to the venous system. However, about half of all DVTs also don’t cause immediate complications—but they remain concerning because they still carry the risk of breaking off and causing pulmonary embolism.[2]
