Deep Vein Thrombosis

Medically Reviewed By William C. Lloyd III, MD, FACS

What is deep vein thrombosis?

Deep vein thrombosis (DVT) is a serious condition in which a blood clot called a thrombus develops in a vein located deep within the body. A deep vein thrombosis usually forms within a large vein in the thigh or calf area, or sometimes the pelvic area. DVT can also develop in the arm, but this is rare.

Your veins are responsible for transporting oxygen-poor blood from the tissues of the body back to the heart. Blood in the veins is under lower pressure than blood in the arteries. Because of this, blood in the veins can pool and form blood clots more easily than in the arteries.

Blood clots are most likely to form in the legs, where the effects of gravity can increase the pooling of blood. This can occur when you are sitting or lying in one position for an extended period of time, such as during recuperation from a disease or surgery. Certain medications and medical conditions can also cause a DVT by increasing the blood’s ability to clot or encouraging the clotting of blood in a vein. Normally, muscle movement in the legs helps move the blood through the veins and reduces the risk of developing blood clots.

DVT can lead to a dangerous, potentially life-threatening complication known as a pulmonary embolism. This occurs when a blood clot breaks off and travels through the blood stream and lodges in the lungs, obstructing blood flow. DVT and pulmonary embolism are major health threats.

DVT and pulmonary embolism are life-threatening emergency conditions. Seek immediate medical care (call 911) if you, or someone you are with, have symptoms of DVT or pulmonary embolism, such as unexplained leg pain or swelling, difficulty breathing, chest pain, or change in consciousness.

What are the symptoms of deep vein thrombosis?

In many cases, a deep vein thrombosis (DVT) can develop without any obvious symptoms. When symptoms do occur, they can include leg pain, warmth, redness or swelling.

A serious complication of DVT is a pulmonary embolism in which the blood clot travels to the lung. The symptoms of a pulmonary embolism are more evident than those associated with DVT. In fact, many people are not diagnosed with DVT until after they develop the hallmark symptoms of a pulmonary embolism, including shortness of breath and coughing blood.

Serious symptoms that might indicate a life-threatening condition

Deep vein thrombosis is a serious condition that can rapidly result in the development of an embolism that travels through the blood stream and obstructs blood supply to the lungs. Seek immediate medical care (call 911) if you, or someone you are with, have any of the following symptoms:

  • Change in level of consciousness or alertness, such as passing out (fainting) or unresponsiveness
  • Coughing blood
  • Rapid heart rate (tachycardia)
  • Unexplained tenderness or cramp-like pain in the thigh or calf, or pain behind the knee, especially if accompanied by increased skin warmth or redness.
  • Weak or absent pulse

What causes deep vein thrombosis?

Deep vein thrombosis (DVT) is a vascular condition that occurs when a blood clot called a thrombus forms in a deep vein within the thigh, calf or pelvis. Blood clots can also develop in the arm and other parts of the body. Blood clots can be caused by diseases, disorders, medical treatments, and conditions that increase the ability of blood to clot, encourage the formation of a clot in a vein, or decrease blood circulation. Poor circulation can allow blood in the veins to pool and increase the risk of clotting.

Causes of DVT include:

  • Chronic illnesses, including heart and lung disease and cancer, which can cause blood to clot easier
  • Conditions that increase the blood’s capacity to clot, including certain rare inherited disorders, nephrotic syndrome, and polycythemia vera (increased production of blood cells that causes thickening of the blood)
  • Immobility due to situations such as bed rest, long periods of sitting or travel, or having a cast
  • Increased estrogen from pregnancy, hormone-based birth control, or hormone replacement therapy. Estrogen increases the levels of clotting factors. Annually, about 1 in 3,000 women taking birth control pills develops a blood clot.
  • Injury to the inner lining of a vein. This can occur due to such factors as surgery, serious fractures, certain medications, needle puncture to the vein, or inflammation caused by vasculitis.

Who gets deep vein thrombosis?

The exact number of people who develop a DVT every year is not known. A DVT is a type of venous thromboembolism (VTE). A pulmonary embolism (PE) is the other type. Some U.S. reports estimate the annual incidence of VTEs is 1 to 2 per 1,000 people, or 300,000 to 600,000 cases a year. However, the actual incidence may be higher because VTE is underdiagnosed.

Clinical data on VTE shows:

  • About two-thirds of VTE cases are DVTs, but the proportion of PEs increases with age. The Society of Vascular Surgery estimates about 300,000 people a year in the United States develop a first-time DVT.
  • The incidence of VTE increases with age. The rate of VTE is less than 1 per 1,000 people age 15 and younger and rises to 5 to 6 per 1,000 people age 80 and older.
  • Incidence of VTE in males is slightly greater than in females, except for women’s childbearing years (defined as 16 to 44), when the rate is higher for women than men.
  • The rate of VTE is higher in White and Black Americans than it is for other ethnicities and races.
  • Approximately 5 to 8% of the U.S. population has at least one genetic risk factor for DVT and PE.

What are the risk factors for deep vein thrombosis?

A number of factors are thought to increase your chances of developing deep vein thrombosis (DVT). Risk factors include a variety of conditions that slow or disrupt the flow of blood in the veins or damage the inside of a vein, resulting in the formation of a blood clot. Your chances of developing deep vein thrombosis increase if you have more than one risk factor including:

  • Advanced age, particularly people older than 60, although individuals of any age can develop deep vein thrombosis
  • Cancer and cancer treatment
  • Fractures, especially in the leg or pelvis
  • Heart and lung diseases
  • Immobility due to situations such as bed rest, long periods of sitting or travel, or having a cast
  • Injuries to deep veins
  • Male gender
  • Medications, such as birth control pills and estrogen. Your risk from these medications increases if you smoke.
  • Obesity
  • Personal or family history of blood clots or diseases that cause blood clots
  • Placement of a catheter in a large vein or having a pacemaker
  • Pregnancy and the postpartum period
  • Recent surgery, especially that of the hip, legs, abdomen, or female reproductive organs

Reducing your risk of deep vein thrombosis

You can reduce your risk of developing deep vein thrombosis by following your treatment plan for such conditions as cancer and heart and lung diseases. You can also lower your risk by:

  • Appropriate use of blood-thinning medication in susceptible individuals
  • Avoiding intravenous (IV) drug use
  • Maintaining a healthy weight and not being overweight or obese
  • Not sitting for long periods without movement, such as when traveling or working at a computer
  • Not smoking
  • Use of compression stockings when bedridden or as a passenger during long-haul air travel

How is deep vein thrombosis diagnosed?

Tests to diagnose a DVT include:

  • Duplex ultrasound, the most common method of diagnosing a DVT. A duplex ultrasound combines regular ultrasound with Doppler technology to track moving objects, such as blood flowing through blood vessels.
  • MRI (magnetic resonance imaging) uses a magnet-based technology to create detailed pictures of blood vessels including the pulmonary arteries.
  • CT (computed tomography) takes multiple X-ray images of the body from different angles to produce a highly detailed image. A CT scan with a contrast agent administered into a vein is CT angiography. The contrast highlights the circulatory system.
  • D-dimer blood test measures fibrin proteins that a blood clot releases when it dissolves. Higher-than-normal levels of fibrin suggest DVT. In case of a positive D-dimer test and signs and symptoms of DVT or PE, the doctor is likely to order CT angiography to confirm the diagnosis.

Additional diagnostic tests may help determine the underlying cause of DVT.

How is deep vein thrombosis treated?

Deep vein thrombosis can be treated and often prevented. Treatment and prevention plans are individualized to the severity of the disease; your age, sex, and medical history; your risk of complications; and other factors. The main treatment goals are to stop the blood clot (thrombus) from growing larger, prevent it from traveling to the lungs, and reduce future clotting risks.

Typically, deep vein thrombosis is treated and may be prevented with medications and other treatments that can include:

  • Anticoagulants, which are medications that “thin” the blood. Anticoagulants prevent new clots from forming or older ones from increasing in size until the body can break down and absorb the clot. Commonly prescribed anticoagulants include heparin and warfarin (Coumadin). When taking anticoagulants, it is important to follow your health care provider’s instructions exactly, because of the possibility for serious side effects such as bleeding. You will need periodic blood tests to determine if a dose adjustment is needed.
  • Compression stockings, which improve blood flow in your legs
  • Thrombectomy, a minimally invasive or open surgical procedure to remove the clot with or without clot-busting medicine (thrombolytic).
  • Thrombolytics, which are medications that can dissolve a clot. Thrombolytics are only used in specific types of serious cases because of the potential for serious adverse effects.
  • Vena cava filter, which is a special type of filter that is placed in the large vein that empties into the heart. The filter catches emboli before they can reach the lungs and cause serious complications.

What are the potential complications of deep vein thrombosis?

Complications of deep vein thrombosis are serious and even life threatening. The most serious threat from DVT is pulmonary embolism (PE).

When an embolus lodges in the lung, it blocks blood flow and prevents freshly oxygenated blood from reaching other parts of the body, including the brain. More than 50,000 people die from PE every year in the United States.

Another DVT complication is post-thrombotic syndrome, which affects nearly one-third of all those with deep vein thrombosis. It is more likely to develop in patients who had a DVT that damaged the walls or valves of the vein. This allows blood to pool in the vein causing such symptoms as long-term swelling of the area, pain, skin discoloration, skin ulcers, and itchiness. Post-thrombotic syndrome can develop weeks, months or even years after the DVT. It can cause chronic problems and significant disability.

Reviews of DVT and PE cases estimate that 6% of DVT and 10% of PE cases are fatal within one month of the episode. The actual rate of PE deaths may be as high as 30%.

How does deep vein thrombosis affect quality of life?

DVT treatment is most effective when the blood clot is caught early. After the clot is dissolved or removed, swelling and pain subside and go away completely. However, people who need long-term anticoagulant therapy are at increased risk for bleeding. They may require regular blood testing to maintain a safe and effective anticoagulant dose, depending on the drug.

After a first-time DVT, people have an increased risk of a second DVT; about 30% of patients have a second event within 10 years, even with standard anticoagulant therapy. Overall, quality of life can be impaired for up to four months or longer after a first-time DVT. One-third to one-half of people with a DVT develop post-thrombotic syndrome.

DVTs and complications put a financial burden on the patient and healthcare system overall. Annual costs for both DVT and PE are estimated at approximately $8,000 to $16,000 per patient based on medical claims data.

Raising deep vein thrombosis awareness

Organizations around the world are working to raise awareness of DVT and PE, particularly prevention in the hospital setting. The National Institutes of Health funds research to advance DVT awareness, prevention, diagnosis and treatment. In 2007, the National Blood Clot Alliance and the Centers for Disease Control and Prevention began the Stop the Clot awareness program.

March is DVT awareness month.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Jan 18
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