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Deep Vein Thrombosis (DVT)

(Deep Venous Thrombosis)


James D. Douketis

, MD, McMaster University

Last full review/revision Feb 2021| Content last modified Feb 2021
Topic Resources

Deep vein thrombosis is the formation of blood clots (thrombi) in the deep veins, usually in the legs.

Venous thromboembolism (VTE) refers to a blood clot that starts in a vein and then breaks free to travel through the circulation, usually to the lungs. ( pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism is the blocking of an artery of the lung (pulmonary artery) by a collection of solid material brought through the bloodstream (embolus)—usually a blood clot (thrombus) or... read more ). Because almost any clot (thrombus) can break loose and become an embolism, doctors sometimes refer to DVT as "thromboembolic disease."

Deep vein thrombosis occurs most often in the legs or pelvis but may also occasionally develop in the arms.

Causes of DVT

Three main factors can contribute to deep vein thrombosis:

  • Injury to the vein’s lining

  • An increased tendency for blood to clot

  • Slowing of blood flow

Injury to the vein

Veins may be damaged during surgery or during an injury to an arm or leg, by the injection of irritating substances, by inflammation, or by certain disorders, such as thromboangiitis obliterans Thromboangiitis Obliterans Thromboangiitis obliterans is inflammation and subsequent blockage of small and medium-sized arteries of the legs or arms. Thromboangiitis obliterans commonly develops in smokers. Symptoms are... read more . They may also be injured by a clot, making formation of a second clot more likely.

Increased blood clotting tendency

Some disorders, such as cancer and certain inherited disorders of blood clotting Overview of Blood Clotting Disorders Blood clotting (coagulation) disorders are dysfunctions in the body's ability to control the formation of blood clots. These dysfunctions may result in Too little clotting, leading to abnormal... read more , cause blood to clot when it should not. Some drugs, including oral contraceptives, estrogen therapy, or drugs that act like estrogen (such as tamoxifen and raloxifene), can cause blood to clot more readily. Smoking is also a risk factor. Sometimes blood clots more readily after childbirth or surgery. Among older people, dehydration commonly causes the blood to clot more readily and can therefore contribute to deep vein thrombosis.

Slowing of blood flow

During prolonged bed rest and other occasions when the legs are not moving normally (such as after a leg injury or a stroke), blood flow slows, because the calf muscles are not contracting and squeezing the blood toward the heart. For example, deep vein thrombosis may develop in people who have had a heart attack Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or a heart attack (myocardial infarction), depending on the location and amount... read more Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) or other serious disorder (such as heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more Heart Failure (HF) , chronic obstructive pulmonary disease Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease is persistent narrowing (blocking, or obstruction) of the airways occurring with emphysema, chronic obstructive bronchitis, or both disorders. Cigarette... read more Chronic Obstructive Pulmonary Disease (COPD) [COPD], or a stroke Overview of Stroke A stroke occurs when an artery to the brain becomes blocked or ruptures, resulting in death of an area of brain tissue due to loss of its blood supply (cerebral infarction) and symptoms that... read more ) and lie in a hospital bed for several days without sufficiently moving their legs or in people whose legs and lower body are paralyzed (paraplegics). Deep vein thrombosis can develop after major surgery, particularly pelvic, hip, or knee surgery. Thrombosis can even occur in healthy people who sit for long periods, for example, during long drives or airplane flights, but thrombosis is extremely uncommon in this circumstance and usually occurs in people with other risk factors.

Did You Know...

  • Although uncommon, thrombosis can occur in healthy people who sit for long periods, such as during long drives or flights.

Complications of DVT

Although deep vein thrombosis is uncomfortable, the main concern is with the complications, including

Pulmonary embolism

A blood clot in a deep vein sometimes can break loose, becoming an embolus. The embolus can travel through the bloodstream, through the heart, and into the lungs, where it lodges in a blood vessel in the lung, blocking blood flow to a portion of the lung. This blockage is called pulmonary embolism Pulmonary Embolism (PE) Pulmonary embolism is the blocking of an artery of the lung (pulmonary artery) by a collection of solid material brought through the bloodstream (embolus)—usually a blood clot (thrombus) or... read more and can be fatal, depending on how large the clot is. The small blood clots that occur in superficial venous thrombosis usually do not become emboli. Thus, only thrombi in the deep veins are potentially dangerous.

Blood clots in the legs or pelvis are more likely to become emboli than blood clots in the arms, perhaps because the squeezing action of the calf muscles can dislodge a blood clot in a deep vein.

The consequences of pulmonary embolism depend on the size and number of emboli:

  • A small embolus may block a small artery in the lungs, causing the death of a small piece of lung tissue (called pulmonary infarction).

  • A large pulmonary embolus can block all or nearly all of the blood traveling from the right side of the heart to the lungs, leading to low blood pressure, low oxygen levels, and quickly causing death.

Massive emboli are not common, but no one can predict which case of deep vein thrombosis, if untreated, will lead to a massive embolus.

Multiple emboli may occur. Multiple emboli typically go to different parts of the lungs. Thus, doctors are greatly concerned about every person who has deep vein thrombosis.

Chronic venous insufficiency

Ischemia (lack of blood flow)

Rarely, a very large blood clot in a leg causes so much swelling that it blocks the blood flow through the leg. The leg becomes pale or blue and extremely painful. Gangrene can develop if the blood flow is not restored.

Symptoms of DVT

About half of the people with deep vein thrombosis have no symptoms at all. In these people, chest pain or shortness of breath caused by pulmonary embolism may be the first indication that a blood clot is present. In other people, if a deep leg vein is involved, the calf swells and may be painful, tender to the touch, and warm. The ankle, foot, or thigh may also swell, depending on which veins are involved. Similarly, if an arm vein is involved, the arm may swell.

Diagnosis of DVT

  • Doppler ultrasonography

  • Blood tests to measure D-dimer

Deep vein thrombosis may be difficult for doctors to detect, especially when pain and swelling are absent or very slight. When this disorder is suspected, Doppler ultrasonography Echocardiography and Other Ultrasound Procedures Echocardiography and Other Ultrasound Procedures can confirm the diagnosis.

Sometimes doctors do a blood test to measure a substance called D-dimer that is released from blood clots. If the level of D-dimer in the blood is not increased, the person probably does not have a deep vein thrombosis.

If the person has symptoms of pulmonary embolism, computed tomography (CT) angiography Chest Imaging or rarely, nuclear lung scanning Chest Imaging using a radioactive marker, is done to detect pulmonary embolism, and Doppler ultrasonography is done to check the legs for clots. These procedures are done except when a person collapses due to very low blood pressure or very low oxygen levels. Collapse suggests massive pulmonary embolism and requires immediate treatment.

Prevention of DVT

Although the risk of deep vein thrombosis cannot be entirely eliminated, it can be reduced in several ways:

  • Prevention of immobility

  • Anticoagulant drugs

  • Intermittent pneumatic compression devices

Preventive measures are selected depending on the person's risk factors and individual characteristics.

People at low risk of deep vein thrombosis, such as those who must be temporarily inactive for long periods, as during an airplane flight, and those who are undergoing minor surgery but have no other risk factors for deep vein thrombosis, can take simple measures. Such people should elevate their legs, flex and extend their ankles about 10 times every 30 minutes, and walk and stretch every 2 hours while awake during long flights.

People at higher risk of deep vein thrombosis require additional preventive treatment. Such people include

  • People undergoing minor surgery who have specific risk factors for deep vein thrombosis (for example, cancer or excessive blood clotting)

  • People without risk factors undergoing major surgery (especially orthopedic surgery)

  • People who are hospitalized with a serious illness (for example a heart attack or serious injury)

Such higher risk people should keep their legs elevated and begin moving around and walking as soon as possible. Additionally, an anticoagulant drug Anticoagulant drugs Deep vein thrombosis is the formation of blood clots (thrombi) in the deep veins, usually in the legs. Blood clots may form in veins if the vein is injured, a disorder causes the blood to clot... read more Anticoagulant drugs , such as heparin, low-molecular-weight heparin, or a newer direct oral anticoagulant can be used. These drugs help prevent deep vein thrombosis by reducing the blood's ability to clot but have a slight risk of causing excessive bleeding.

Alternatively, intermittent pneumatic compression (IPC) leggings are an effective way to prevent clots in higher risk people, particularly those who are having surgery associated with a high risk of bleeding or who just had a serious injury and thus should not use an anticoagulant drug. Usually made of plastic, these leggings are automatically pumped up and emptied by an electric pump. They repeatedly squeeze the calves and empty the veins. The leggings are put on before surgery and kept on during and after surgery, until the person can walk again.

Continuously wearing high-compression elastic stockings (support hose) makes the veins narrow slightly and the blood flow more rapidly. As a result, clotting may be less likely. However, elastic stockings are not sufficient protection against developing deep vein thrombosis. Also, they may give a false sense of security and discourage more effective methods of prevention. If not worn correctly, they may bunch up and aggravate the problem by blocking blood flow in the legs.

Treatment of DVT

  • Anticoagulant drugs (sometimes called blood thinners)

  • Clot-dissolving drugs

For deep vein thrombosis, a doctor’s main goal is to prevent pulmonary embolism. Hospitalization may be necessary at first, but because of the advances in treatment, most people with deep vein thrombosis can be treated at home. Bed rest is unnecessary except to help relieve symptoms. People may be as active as they want. Physical activity does not increase the risk that a blood clot will break loose and cause a pulmonary embolism.

Treatment usually consists of

  • Anticoagulant drugs (most common)

  • Clot-dissolving drugs

  • Rarely, a clot-blocking filter (umbrella)

Did You Know...

  • People with deep vein thrombosis may be as active as they want. Physical activity does not increase the risk that a blood clot will break loose and cause pulmonary embolism.

Anticoagulant drugs

All people with deep venous thrombosis are given anticoagulant therapy. Doctors usually use low-molecular-weight heparin (such as enoxaparin, dalteparin, or tinzaparin) or fondaparinux given by injection under the skin (subcutaneously), accompanied by warfarin taken by mouth. The injectable drug works immediately, but warfarin takes several days to be fully effective. Once the warfarin has taken effect, people stop taking the injectable drug. For some people (those with cancer or those with recurrent clotting problems despite treatment with anticoagulants by mouth), doctors simply use the injectable drug and do not start warfarin.

How long people continue drug treatment (with warfarin or an injectable drug) varies according to the degree of risk. People whose deep vein thrombosis resulted from a specific, temporary cause (such as surgery or a drug they have stopped taking) usually continue anticoagulant therapy for 3 to 6 months. When a specific cause is not found, people usually take warfarin for at least 6 months. Warfarin should be continued indefinitely if the cause is not temporary (for example, a blood clotting disorder) or if people have had two or more episodes of deep vein thrombosis.

Use of warfarin increases the risk of bleeding, both internally and externally. To minimize the risk, people taking warfarin must have periodic blood tests to see how much their blood is anticoagulated. Doctors then use the blood test result to adjust the dose of warfarin. The blood tests are usually done once or twice a week for 1 or 2 months, and then every 4 to 6 weeks thereafter. Many different drugs and foods change how the body breaks down warfarin (see also Drug Interactions Drug Interactions The effect a drug has on a person may be different than expected because that drug interacts with Another drug the person is taking (drug-drug interaction) Food, beverages, or supplements the... read more ). Some drugs and foods increase its breakdown, making a warfarin dose less effective and increasing the risk of another blood clot. Other drugs and foods slow warfarin's breakdown, making a dose more effective and thus more likely to cause bleeding. Some people are also more sensitive to warfarin and may need warfarin sensitivity testing to help doctors adjust their levels.

There are newer drugs given by mouth that doctors may use as an alternative to warfarin. These drugs, called direct oral anticoagulants (DOAC), include rivaroxaban, apixaban, edoxaban, and dabigatran etexilate. These drugs have a faster anticoagulant effect than warfarin and are as effective as warfarin for the treatment of blood clots. For these newer drugs people do not need to have frequent blood tests in order to adjust the dose as they do with warfarin, but the risk of bleeding is still increased.

Excessive bleeding, which may be life-threatening, is the most common complication of anticoagulant drugs. Risk factors for excessive bleeding include

For people who are taking warfarin, doctors can give vitamin K, transfusions of plasma (which contains clotting factors), or prothrombin complex concentrate to reverse the anticoagulation. For people who are taking low molecular weight heparin, doctors can give protamine to partially reverse the anticoagulation.

The newer direct oral anticoagulants (DOACs) (apixaban, dabigatran, edoxaban, and rivaroxaban), which are taken by mouth, tend to cause fewer episodes of serious bleeding than warfarin, but currently antidotes for these drugs are not widely available if excessive bleeding does occur. Doctors are testing additional antidotes.

Clot-blocking filter

Very rarely, if anticoagulants cannot be tolerated, have caused serious side effects, or have failed to prevent more clots, a filter (umbrella) can be placed inside a large vein between the heart and the area affected by deep vein thrombosis. Usually if a filter is placed, it is inserted into the inferior vena cava, which returns blood to the heart from the lower part of the body. A filter can trap emboli, preventing them from reaching the lungs but unlike anticoagulant drugs, filters do not prevent new clots from forming. Filters are usually reserved for people in whom anticoagulant therapy is not possible or not effective.

Inferior Vena Cava Filters: One Way to Prevent Pulmonary Embolism

In people who have deep vein thrombosis, a blood clot may break loose from an affected vein in the leg and travel through the bloodstream. A clot that breaks loose is called an embolus.

The embolus travels toward the heart and passes through the right atrium and ventricle and into one of the pulmonary arteries, which carry blood to the lungs. The clot may lodge in an artery in a lung and block blood flow, resulting in pulmonary embolism. Pulmonary embolism may be life threatening, depending on the size of the blocked artery.

To prevent pulmonary embolism, doctors usually use drugs that limit blood clotting. However, for some people, doctors may recommend that a filter (formerly called an umbrella) be temporarily or permanently placed in the inferior vena cava. This filter device typically is recommended when drugs that limit clotting (anticoagulants, or blood thinners) cannot be used, for example, when a person is also having bleeding. The filter can trap emboli before they reach the heart but allow blood to flow through freely. Emboli that are trapped sometimes dissolve on their own.

However, filters do not completely eliminate the risk of emboli. Sometimes other veins from the legs enlarge, allowing blood and emboli to bypass the filter. Also, filters can break loose or become blocked by a clot. Filters are much less effective at preventing pulmonary embolism than treatment with anticoagulants.

Inferior Vena Cava Filters: One Way to Prevent Pulmonary Embolism

Clot-dissolving drugs

Doctors only occasionally use intravenous drugs, such as alteplase, to dissolve venous blood clots. These drugs (also called thrombolytic, fibrinolytic, or clot-busting drugs) may be given if the blood clot has been present for less than 48 hours. After 48 hours, scar tissue begins to develop in the blood clot, making it less likely to dissolve. Clot-dissolving drugs have a higher risk of bleeding complications.

Doctors sometimes use clot-dissolving drugs in combination with mechanical removal methods in people who have large clots in their upper leg. In such cases, doctors may put a small, flexible tube (catheter) into the blocked vein, remove as much clot as possible with an instrument, and administer the clot-dissolving drug through the catheter.

Treatment of complications

If pulmonary embolism Treatment Pulmonary embolism is the blocking of an artery of the lung (pulmonary artery) by a collection of solid material brought through the bloodstream (embolus)—usually a blood clot (thrombus) or... read more occurs, treatment usually includes oxygen (usually given by a face mask or nasal prongs), analgesics to relieve pain, and anticoagulant drugs. If pulmonary embolism is life threatening, clot-dissolving drugs are given or surgery is done to remove the embolus.

If painful skin ulcers ( venous stasis ulcers Chronic Venous Insufficiency and Postphlebitic Syndrome Chronic venous insufficiency is damage to leg veins that prevents blood from flowing normally. Postphlebitic syndrome is chronic venous insufficiency that results from a blood clot in the veins... read more Chronic Venous Insufficiency and Postphlebitic Syndrome ) develop, properly applied compression bandages can help. When these bandages are applied carefully once or twice a week, the ulcer almost always heals because blood flow in the veins improves. The ulcers can become are infected, and pus and a foul-smelling discharge can appear on the bandage each time it is changed. The pus and discharge can be washed off the skin with soap and water. Skin creams, balms, and skin medications of any kind have little effect.

Once blood flow in the veins has improved, the ulcer heals by itself. After it has healed, wearing an elastic stocking daily can prevent a recurrence. The stocking must be replaced as soon as it becomes too loose. If possible, the person should purchase seven stockings or pairs of stockings (if both legs are involved)—one for each day of the week so that stockings remain effective considerably longer.

Rarely, ulcers that do not heal require skin grafting. After grafting, an elastic stocking must be worn to prevent ulcers from returning.

More Information

The following is an English-language resource that may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

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