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Deep vein thrombosis

What is it, Causes, Prevention, and More

Author: Anna Hernández, MD

Editors: Alyssa Haag, Ahaana Singh, Emily Miao, PharmD

Illustrator: Jillian Dunbar

Copyeditor: David Walker


What is deep vein thrombosis?

Deep vein thrombosis, or DVT, occurs when a blood clot, or thrombus, develops in one of the large veins of the upper or lower limbs. These veins typically run deep between muscles, as opposed to superficial veins, which lie closer to the skin. Most commonly, DVTs involve one of the deep veins of the lower limb, such as the proximal iliac veins, femoral veins, or the distal popliteal veins. Rarely, though, venous blood clots can form in the upper limb, usually in individuals with indwelling intravenous catheters (i.e., a device that allows repeated and long-term access to the bloodstream). 

One of the most dangerous complications of DVT is pulmonary embolism (PE), which occurs when increased blood pressure in the vein causes parts of the venous blood clot to break off and travel to the lungs. This is a potentially life-threatening situation that prevents blood from entering the lungs to receive oxygen, resulting in sudden shortness of breath and chest pain. Other complications of DVT include recurrent venous thromboembolism, post-thrombotic syndrome, and bleeding as a result of anticoagulant therapy.


What causes deep vein thrombosis?

Deep vein thrombosis typically occurs as a result of a combination of risk factors that increase the risk of developing thrombosis. These factors are collectively known as Virchow’s triad, and include hypercoagulability, slowed venous blood flow, and damage to the inner lining of blood vessels. 

Hypercoagulability occurs when there is an increased tendency of a person’s blood to clot more quickly. This can occur due to genetic conditions, such as with factor V Leiden or with antithrombin III deficiency, or due to acquired reasons, such as after a surgery or when taking certain medications, such as hormone replacement therapy or birth control pills

Another factor is stasis of blood, which occurs when blood flow becomes slow and turbulent, and static pockets of blood are formed. Stasis can happen during long periods of inactivity, such as with prolonged bed rest, long flights and car rides, and during pregnancy when the growing baby compresses nearby veins and reduces venous return to the heart. 

Finally, damage to the inner lining of blood vessels can trigger the activation of the coagulation cascade, leading to the formation of a blood clot inside the blood vessel. This type of damage can be caused by some kind of trauma or injury; atherosclerosis; infections; chronic inflammation; or toxins, like those found in tobacco cigarettes. 

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What are the warning signs of deep vein thrombosis?

Warning signs of DVT can include a throbbing or cramping pain in the affected limb, usually in the calf or thigh; swelling; warm skin around the painful area; and swollen veins that are hard or sore to the touch.

What are the signs and symptoms of deep vein thrombosis?

Signs and symptoms of DVT vary depending on the extent and location of the blood clot. In some cases, DVT can develop silently; however, the most common symptoms include redness, swelling, and pain on the affected limb. Since DVT often affects the lower leg, a typical sign on physical examination is a larger calf diameter relative to the unaffected leg. Another classic finding is the Homan’s sign, which occurs when the individual experiences calf pain upon passive dorsiflexion of the foot (i.e., raising the foot towards the shin), but this sign isn’t always present and is not diagnostic of DVT.

How is deep vein thrombosis diagnosed?

Diagnosis of DVT begins by taking a thorough medical history and performing a physical exam. If a DVT is suspected, a Wells score can be obtained to determine the pretest probability of DVT, which is the likelihood that an individual has a DVT before any further testing occurs. The Wells score takes into account the individual’s current signs and symptoms, as well as the presence of certain risk factors that increase the risk of thrombosis (e.g., prior history of DVT, prolonged immobilization, active cancer, etc.). 

If the probability of DVT is high, diagnosis typically involves conducting an ultrasound of the affected limb. On the other hand, if the probability of DVT is low, a D-dimer blood test can be used to rule out DVT as the diagnosis. D-dimer is a product of fibrin degradation that becomes elevated when blood clots are actively forming in the body. If the D-dimer is low, no further testing is needed to rule out DVT, and if the D-dimer is elevated, the diagnosis of a DVT can be confirmed with an ultrasound. Many other conditions (e.g., cancer, sepsis, and pregnancy) can present with an elevated D-dimer, and therefore, the D-dimer test is very useful to exclude DVT but cannot be relied on to confirm DVT diagnosis.


How is deep vein thrombosis treated?

Deep vein thrombosis can be treated with blood thinners, like heparin, warfarin, or direct anticoagulants (e.g., rivaroxaban and apixaban). These medications work by inhibiting the clotting cascade, thereby preventing blood from clotting. In severe cases, such as with extensive blood clots or involvement of the proximal iliac veins, thrombolytic enzymes can be given to help break down the clot. Alternatively, a thrombectomy can be performed to surgically remove the clot. 

After the acute episode of DVT has resolved, some individuals can develop post-thrombotic syndrome as a result of the damage caused to the veins. Common symptoms include chronic leg swelling, skin discoloration, and leg ulcers. Early treatment of DVT can sometimes prevent this complication, although predisposed individuals may develop post-thrombotic syndrome even after receiving appropriate treatment. 

How is deep vein thrombosis prevented?

DVTs can be prevented by using compression stockings and doing frequent calf exercises during long periods of inactivity in order to help blood move through the veins and prevent stasis. Additionally, individuals with a higher risk of DVT or PE and lower risk of bleeding may be given long-term anticoagulant therapy.

What are the most important facts to know about deep vein thrombosis?

Deep vein thrombosis (DVT) refers to a blood clot found in a deep vein, particularly in one of the large leg veins. The three main factors that increase the risk of DVT are hypercoagulation of clotting factors, stasis of blood, and damage to the inner lining of blood vessels. In particular, specific risk factors include smoking tobacco; being pregnant; having an inflammatory condition, such as cancer; and prolonged immobilization. Signs and symptoms of DVT include redness, pain, and swelling on the affected limb. Diagnosis is typically done by ultrasound. A D-dimer test can be conducted to rule out a DVT as the diagnosis if the clinical presentation is unclear. Treatment of DVT can include anticoagulant therapy, thrombolysis, or thrombectomy. 

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Related links

Artery and vein histology
Deep vein thrombosis
Deep vein thrombosis and pulmonary embolism: Pathology review
Thrombosis syndromes (hypercoagulability): Pathology review

Resources for research and reference

Jameson, J. L. (2018). Harrison's principles of internal medicine. McGraw-Hill Education. 

Kahn S. R. (2016). The post-thrombotic syndrome. Hematology. American Society of Hematology. Education Program, 2016(1), 413–418. DOI: 10.1182/asheducation-2016.1.413

Ortel, T. L., Neumann, I., Ageno, W., Beyth, R., Clark, N. P., Cuker, A., … Zhang, Y. (2020). American Society of Hematology 2020 guidelines for management of venous thromboembolism: treatment of deep vein thrombosis and pulmonary embolism. Blood Advances, 4(19), 4693–4738. DOI:10.1182/bloodadvances.2020001

Stone, J., Hangge, P., Albadawi, H., Wallace, A., Shamoun, F., Knuttien, M. G., Naidu, S., & Oklu, R. (2017). Deep vein thrombosis: pathogenesis, diagnosis, and medical management. Cardiovascular diagnosis and therapy, 7(Suppl 3), S276–S284. DOI:10.21037/cdt.2017.09.01