What is venous thromboembolism?
A venous thromboembolism is a blood clot that blocks the flow of blood. "Thrombo" means blood clot, and "embolism," means a circulating particle that causes an obstruction. "Venous" means in the veins. When healthcare providers talk about venous thromboembolism (VTE), they often talk about it as a disorder that can lead to two different kinds of blood clotting conditions: deep vein thrombosis and pulmonary embolism.
Veins carry blood from the extremities of your body back to your heart. When a vein is blocked, blood pools behind the blockage, causing inflammation, and cells ahead of the blockage can’t get the oxygen and nutrients they need. This can do serious damage to the veins, tissues and organs that they feed. In some cases — such as when a VTE blocks blood flow to the lungs — it can be life-threatening.
How does venous thromboembolism occur?
Blood clotting is a normal and healthy response to a superficial cut or wound. Your blood coagulates — partially solidifies — in order to keep it from leaking too fast from a hole. On the outside of your body, this produces a scab. On the inside of your body, it produces a clot. Blood clotting can also be triggered by an infection, which irritates the lining of the blood vessel like a wound. When the wound or infection begins to heal, the clot is supposed to dissolve. But sometimes it doesn’t. And sometimes blood clots form when there was no wound. Many factors can contribute to this. If the clot is big enough, it can block the vein.
How does venous thromboembolism affect my body?
A venous thromboembolism is not the type of blood clot that typically causes a heart attack or stroke. Those are usually caused by blood clots in your arteries, not in your veins. But a VTE can be just as dangerous. The most serious complications occur when a VTE breaks loose from where it formed, travels through your bloodstream, and gets stuck in the veins of your lungs. This is called a pulmonary embolism (PE). A PE restricts oxygen and blood flow to your lungs while increasing blood pressure in your arteries. This causes pulmonary hypertension, which in turn can cause heart failure and death.
VTEs usually form in the deeper veins of your body, embedded in the muscles of your legs or arms. When a blood clot is stuck in your deeper veins, it’s called a deep vein thrombosis (DVT). A DVT that blocks the vein causes inflammation at the site of the blockage and can cause long-term damage to the vein, resulting in chronic venous insufficiency (post-thrombotic syndrome). Not all DVTs cause an obstruction, but because they can, they are considered a venous thromboembolic disease. DVTs can also break loose and travel to your lungs, leading to pulmonary embolism (PE).
What is the difference between a thrombosis and a thromboembolism?
A thrombosis is a blood clot. A thromboembolism is a circulating blood clot that gets stuck and causes an obstruction. Both deep vein thrombosis and pulmonary embolism are included under the umbrella term of venous thromboembolic diseases because both have the potential to obstruct blood flow in your veins. Blood clots that occur in the smaller, superficial veins close to your skin (superficial venous thrombosis) don't tend to cause the same kinds of complications. About half of DVTs don’t cause complications either, but they can, and they remain a risk factor for PE.
How common is VTE?
In the U.S., VTE is the third most common vascular diagnosis after heart attack and stroke. It affects about 1 in 1,000 Americans each year. About half of people with VTE experience a pulmonary embolism. About 25% of those who have a pulmonary embolism die from it. After the age of 40, your risk of VTE almost doubles every decade.
Who does venous thromboembolism affect?
Anyone can get a VTE, but certain factors put you more at risk. About 25% to 50% of cases arise without obvious cause. Another 20% are associated with cancer, and 20% with surgery. Some people also have blood clotting disorders that make them more prone to clots.
Symptoms and Causes
What causes venous thromboembolism?
Blood clots can occur for many reasons, and no one factor makes them more likely to be big enough to obstruct a vein, or to break loose and travel to your lungs. Anyone who is at risk of blood clotting is at risk of venous thromboembolism. And anyone who is at risk of a VTE is at risk of a pulmonary embolism. People who develop VTEs often have more than one risk factor contributing to the condition.
Some people have an imbalance of blood-clotting proteins, which makes their blood more prone to clot and less prone to dissolve clots (thrombophilia). This can be inherited, or it can be a side effect of a specific condition. Sometimes a lack of movement causes your blood to slow down too much in your veins and it starts to coagulate. This can come from long-distance travel or a sedentary lifestyle.
The most natural cause of blood clotting is injury or infection. Sometimes the injury comes from a medical intervention, like surgery or chemotherapy or inserting an IV or catheter. People who are in the hospital for a long time are more at risk of clotting, because they may be healing from a wound or infection and also subject to invasive medical interventions, and also immobilized in a hospital bed.
What risk factors contribute to venous thromboembolism?
- Injury to a vein, due to bone fracture or surgery.
- Slow blood flow from immobilization.
- Genetics and family history of VTE.
- High estrogen due to pregnancy, birth control or hormone replacement therapy.
- Blood clotting conditions, including Factor V Leiden disease, polycythemia vera and sickle cell disease.
- Certain chronic illnesses, including cancer, heart disease and inflammatory bowel disease (IBD).
- Lifestyle factors, including smoking, obesity and lack of exercise.
- Age (VTE is most common in seniors, perhaps due to higher rates of illness and lifestyle factors.)
What are the symptoms of venous thromboembolism?
Signs of an obstructive DVT occur at the site of the clot. They can include:
Signs of a PE may occur without any previous signs of DVT. They can include:
Diagnosis and Tests
How is VTE diagnosed?
Other conditions can have similar symptoms to DVT and PE. To confirm that you have a venous thromboembolic disease, your healthcare provider will ask about your medical history to identify risk factors of VTE and rule out other possible conditions. They might take a preliminary blood test to look for markers of blood clotting. Then they will use imaging tests to try and locate the blockage.
What tests are used to diagnose venous thromboembolism?
Different tests are used to diagnose DVT and PE.
Tests to diagnose DVT include:
- Blood tests: A blood test called a D-dimer test measures levels of a substance that is released when blood clots dissolve. High levels of the substance may be an indication of blood clotting. Blood tests can also measure oxygen levels in your blood and screen for inherited clotting disorders.
- Vascular ultrasound: This noninvasive imaging test is usually the first choice for visualizing the veins and the flow of blood through them. It’s sometimes called a “duplex ultrasound” because it has two parts. In the first part, the sonographer uses a wand to bounce sound waves off of the veins, producing real-time images on a screen. They might try to compress the vein to see if it collapses normally or if it is stiff with clotting. In the second part, the sonographer bounces sound waves off of the blood in the vein to see how it is flowing. When blood is flowing normally, it changes the sound waves through something called the “Doppler effect."
- MR venography: Magnetic resonance imaging can be more reliable than ultrasound for examining your pelvis, abdomen and chest. MR venography uses pulses of radio-frequency waves to detect blood clots. You will have to lie inside a standard MRI machine for this test. The technician may inject a contrast dye into your veins to make them show up better.
- Contrast venography: This traditional X-ray test requires a contrast dye to be injected into your vein to make it show up in images. It’s more invasive than other imaging tests, but it is considered more accurate and may be used if other tests are inconclusive. An X-ray technician will insert a tiny tube into one of your large veins and then thread it up into the area they want to photograph to deliver the contrast dye. Then they'll take X-rays.
Tests to diagnose PE include:
- Pulse oximetry: If your symptoms indicate PE, your healthcare provider might start by putting a pulse oximetry sensor on the end of your finger to measure oxygen levels in your blood. Low oxygen levels could be caused by PE or by another lung or heart condition.
- Chest X-ray: A chest X-ray won’t diagnose PE, but it can diagnose other possible causes of your symptoms, including lung and heart conditions.
- CT pulmonary angiography (CTPA): This is the standard test for PE. The computed technology (CT) scan produces 3-D imaging of the veins and arteries of your lungs. “Pulmonary” means of the lungs, and “angiography” means X-rays of blood vessels. The CTPA is noninvasive, but it might require contrast dye to be injected into your veins.
- Pulmonary angiogram: When other tests are inconclusive, a traditional pulmonary angiogram will offer definitive results. It is more invasive, though. For this angiogram, an X-ray technician will insert a tube into one of your large veins and then thread it up into your chest area to deliver contrast dye. Then they’ll take X-rays.
Management and Treatment
How is venous thromboembolism treated?
Venous thromboembolism treatment options vary depending on how threatening the clot is. Some DVTs may be managed with oral medications, while some PEs may need to be urgently removed. Your healthcare provider might remove a life-threatening PE through a catheter in your vein, or they might inject a medication called a thrombolytic that dissolves the clot quickly. Because of possible complications, though, these interventions are reserved for emergencies.
When a VTE is not immediately life-threatening, treatment focuses on preventing existing clots from getting bigger and new clots from forming. Preventative treatments include anticoagulants (blood thinners) that reduce clotting and compression stockings that encourage circulation. For trickier cases, your healthcare provider might suggest a physical intervention, such as installing a filter in the vein to keep clots from reaching the lungs.
How can I prevent VTE?
Venous thromboembolism has many risk factors, and not all of them can be managed. But in general, movement is the easiest prevention. Since most DVTs occur in the legs, you can mitigate a lot of risk by keeping blood circulating in your legs. If you sit a lot for work or travel, make sure to get up and walk or exercise your leg muscles periodically to keep blood from pooling. If you’ve been sick or you’re recovering from surgery, getting up and moving as soon as you can will help reduce the risk of clots. Exercise will also help you keep stress levels down and maintain a healthy weight, which are other contributing factors.
How should I take care of myself after a venous thromboembolism?
- Receive routine follow-up care. Your healthcare provider will want to monitor your condition to decide how long you should continue taking medications.
- Take medications as prescribed, unless you notice excessive bleeding, which is a serious side-effect of blood thinners. If you do, stop using them and contact your healthcare provider.
- Check for signs of clotting, including swelling and tenderness, especially in your legs.
- Make healthy lifestyle changes. Stay active and hydrated, manage stress and quit smoking or using tobacco products.
A note from Cleveland Clinic
So many different things can contribute to a venous thromboembolism. You may have risk factors that you weren’t aware of or that you can’t change. However, there’s a lot you can do to prevent a VTE, and manage it effectively if it does occur. If you’re concerned, talk to your healthcare provider about your particular risk factors and how to mitigate your risk. If you do notice symptoms of a VTE, seek medical care right away. We take all blood clots seriously, the ones you have now and the ones you may have.
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