Heart Information Center


Deep venous thrombosis, also known as DVT, is a blood clot in a deep vein of the upper (arm or neck) or lower (leg or pelvic) extremities.

A blood clot from a DVT can break loose (embolize) and travel to the heart or lungs. An embolus can be life threatening.

It is estimated that over half a million hospital patients in the United States develop a DVT each year, causing 50,000 deaths a year due to pulmonary (lung) emboli.

Superficial thrombophlebitis is the name for a blood clot in a vein just below the skin, such as a varicose vein. This is almost never a life threatening condition. Deep venous thrombosis is not the same as superficial thrombophlebitis. Deep veins, in which a DVT occurs, can not be seen or felt under the skin.


What causes a DVT?

Three factors increase the chance of having a DVT:

  1. Injury to a deep vein from trauma or surgery
  2. Poor blood circulation in the deep veins
  3. Conditions that increase the tendency of blood to clot

Injury to a deep vein from trauma or surgery causes release of substances that activate the clotting system.

Blood that is not moving (stagnant)is much more likely to clot. Conditions that can cause poor circulation in deep veins include:

  • Congestive heart failure
  • Prolonged immobilization ( not walking or moving)
  • Preexisting small clots

The body produces a number of clotting factors (many are made in the liver), maintaining a fine balance between factors that cause blood to clot and those that either prevent or dissolve blood clots. Clotting is needed to prevent excessive bleeding when blood vessels are injured. When clotting is no longer needed other clotting factors help dissolve clots. When this balance is disturbed either excessive bleeding or clotting of blood that serves no useful purpose may occur. Increased blood clotting (hypercoagulability) may be caused by:

  • Hormones (birth control pills, pregnancy)
  • Cigarette smoking
  • Certain cancers
  • Inherited deficiencies of anticlotting factors
  • Certain autoimmune disorders


Who gets a DVT?

DVT is more likely to occur in two different situations:

  1. Major surgery, particularly hip and knee replace, increases the risk of DVT due to venous injury and immobilization. This is true even in patients without any other risk factors for DVT. Persons affected are generally older.

  2. Persons with inherited deficiencies of anticlotting factors are at greatly increased risk of DVT. Persons with such deficiencies often develop DVT at a much younger age (20's to 40's) without major surgery or leg trauma, suffer recurrent DVTs, and have family members who have had DVTs. Factor deficiencies, which can be mild or severe, may include:
    • Leiden factor 5 (most common)
    • antithrombin
    • protein C and/ or protein S

Persons with inherited anticlotting factor deficiency and additional risk factors (smoking, pregnancy, birth control pills and /or immobilization) are thought to have a greatly increased risk of developing DVT.


What are the symptoms of a DVT?

Symptoms of a DVT are variable, occurring in less than half of persons with DVT.

Symptoms, depending on the size and location of a DVT, can include:

  • warmth, swelling, redness, and /or pain in a leg.
  • DVT of the calf may cause symptoms in the calf while that in the thigh can cause symptoms in both the thigh and/or calf.
  • The vast majority of DVTs occurs in only one leg at a time

Other medical conditions can cause pain and/ or welling in the legs. Persons with pain and/ or swelling of the legs should see their doctor or go to an emergency department for evaluation, especially if they have DVT risk factors.


Is a DVT serious?

A DVT can be lifethreatening if a large enough blood clot breaks loose and travels to the heart or lungs. Pulmonary emboli (blood clots traveling to the lungs) occur in over 300,000 persons each year in the United States killing at least 50,000 Americans each year. Pulmonary emboli can disrupt blood flow to the lungs by directly blocking blood flow to part of the lung and by triggering certain reflexes that can cause the heat to suddenly stop beating. Many, although not all, pulmonary emboli are caused by embolization of DVTs.

Symptoms of a pulmonary embolus may include:

  • Shortness of breath
  • Chest pain
  • Increased heart and breathing rate.
If these symptoms occur, especially with DVT symptoms, call 911 immediately!

Another complication of DVT, particularly recurrent DVTs, is postphlebitic syndrome. Chronic stretching and injury to deep veins may cause blood to pool and stagnate in the lower legs. This can cause chronic swelling and pain in the affected leg. Leg sores may also develop. Although not life threatening this condition can be unpleasant.


How does a Doctor diagnose a DVT?

Your doctor or an emergency physician may order certain tests if he/she suspects, based on symptoms and risk factors, you might have a DVT. Several different tests can be used to diagnose or exclude a DVT.

Doppler ultrasound is most commonly used. This tests, using sound waves to create a picture of the veins, is very accurate and noninvasive. It is able to reliably detect DVTs in either below or above the knee.

Venogram uses dye injected into the veins followed by a series of x-rays. Although this test is extremely accurate it has largely been replaced by ultrasound because a venogram is more difficult to perform, more expensive, and is somewhat invasive.

Impedance plethsmography (IPG) is very accurate for excluding DVT above the knee( the kind that can embolize to the lungs). It measures volume and pressure changes that occur in the thigh with DVT. IPG is much less accurate in detecting clots below the knee. This limitation is not as important because DVTs below the knee almost never embolize. This test, although inexpensive and accurate, has largely been replaced by ultrasound in most hospitals.


How is a DVT treated?

Treatment of a DVT may depend on both its location and underlying cause. Anticoagulants (blood thinners), which keep the clot from getting larger, are the mainstay of DVT treatment. In certain circumstances clot dissolving (thrombolytic) medications may be used.

Location of DVT

DVT occurring in only the calf (below the knee) rarely embolize. Treatment consists of bedrest at home and anti-inflammatory medications. Anticoagulants are not needed unless the DVT continues to spread (propagate) into the veins of the knee or thigh. Clot propagation occurs in 10 percent to 30 percent of DVTs below the calf. For this reason your doctor will follow you closely and want to know if pain or swelling occur at or above the knee.

Your doctor may hospitalize you if there are risk factors for propagation such as previous DVTs, being bedridden, or having a hypercoagulable disorder.

DVT occurring in deep knee or thigh veins, known as proximal DVT, require hospitalization and anticoagulation because of increased risk of pulmonary embolus.


Once proximal DVT is diagnosed you will be hospitalized for 7 to 10 days and treated with anticoagulants (blood thinning medications). Anticoagulants stop the formation of new clots but do not dissolve already formed clots. Naturally occurring thrombolytic proteins are responsible for slowly dissolving blood clots.


Is an anticoagulant that is given through an IV for the first 5 to 7 days. Heparin works immediately and stops working quickly after being stopped. Unfortunately, heparin cannot be taken by mouth, requires very frequent monitoring, and must be given in a hospitalized setting. Heparin must be continued until a second anticoagulant, coumadin, is working properly.


Coumadin (warfarin) is an anticoagulant that can be taken by mouth. It is started on the first or second day that heparin is started. Coumadin takes about one week to adequately inhibit clotting factors. Heparin must be taken until coumadin is fully effective. Coumadin cannot be used in pregnancy because it crosses the placenta and can cause fetal malformations.

Your doctor will measure certain blood tests, called a PT and a PTT to see how well coumadin and heparin are working.

Low Molecular Weight Heparin

Newer forms of heparin can be self administered under the skin and do not require constant monitoring. Enoxaprin is currently approved by the FDA in the United States for treatment of DVT. Used in Europe for over 10 years, low molecular weight heparins have been shown to be as effective as traditional heparin in DVT prevention and treatment. Because frequent monitoring is not needed hospital stays can be reduced to 2 or 3 days compared to 7 to 10 days currently needed. Benefits include lower health care costs and patient convenience. Larger studies will be needed before Enoxaprin and other low molecular weight heparins gain wider acceptance in the United States.

Coumadin is taken the same way as with IV heparin.

Thrombolytic Medications

Thrombolytic (clot busting) medications, unlike anticoagulants, are able to dissolve blood clots that have already formed. Several types of thrombolytic medications, including TPA and streptokinase, are used to dissolve blood clots that cause heart attacks and DVT.

Use of thrombolytics in DVT has more limited benefit than with heart attack. These medications have increased risk of serious bleeding and are not likely to significantly benefit most persons with DVT because most persons do quite well with proper use of anticoagulants.

Early use of thrombolytics may decrease the incidence of postphlebitic syndrome in persons with massive or recurrent DVT. Clear cut indications for thrombolytic therapy in DVT are still investigation.

Side effects of anticoagulant and thrombolytic medications

Anticoagulants can cause both minor and serious side effect- most related to bleeding. Persons taking anticoagulants must notify their doctor if the following occur:

  • Back or stomach pain
  • Black tarry stools or obvious blood in stools (bowel movements)
  • Vomiting or coughing up blood
  • Blood in the urine
  • Nose bleeds
  • Unusual bruising of the skin , mouth, lips or gums
  • Very heavy menstrual bleeding
  • Cold, blue or painful hands or feet.

Small amounts of blood in the urine and nose bleeds are relatively common when starting anticoagulant therapy. Treatment is not usually stopped for these two problems but your doctor may check blood tests to make sure you are not receiving too much anticoagulant.

Vomiting or passing blood in the stool is potentially a very serious problem and will require immediate evaluation by your doctor or emergency department.

Thrombolytic medications may be used to treat an initial DVT but are not given on an ongoing basis. Side effects are similar to anticoagulants except there is an even higher risk of initial hemorrhage (severe life threatening bleeding) including stroke.

If you are taking anticoagulants it is extremely important you discuss side effects and other medications you may be taking with your doctor in more detail!


How long are anticoagulants taken after a DVT?

DVTs of the knee, thigh and groin (proximal DVTs) are initially treated with intravenous heparin for the first 5 to 10 days in conjunction with coumadin (taken be mouth). How long coumadin is taken will depend on how much risk there is of developing another DVT.

If you have no major risk factors, have not had a DVT and are about to undergo hip or knee replacement you may be anticoagulated for 6 to 12 weeks.

Persons having a DVT are typically anticoagulated for 3 to 6 months. Persons with recurrent DVT, multiple risk factors or severe anticlotting factor deficiency(s) may require lifelong anticoagulation.


How can DVT be prevented?

Prevention of DVT depends on recognizing and eliminating preventable risk factors, such as smoking and extreme obesity, with use of anticoagulants in high risk situations.

Anticoagulation with heparin and coumadin should be used in all persons (not having absolute contraindications) undergoing hip or knee replacement because of the high risk of DVT (30 to 50 percent) when anticoagulation is not used.

Persons who are bedridden, in the hospital or at home, are at increased risk for DVT. The risk is not as high as it is for persons undergoing hip or knee replacement. Injection of subcutaneous heparin (traditional heparin) is effective in preventing (not treating) DVT in this situation. Properly fitted compression stockings (not pantyhose) may also help but are inconvenient and must be used properly.

Persons with recurrent DVTs may require lifelong anticoagulation with coumadin.

All persons taking anticoagulants must be under the care of a physician and undergo routine monitoring.



Anticoagulant a substance that prevents blood from clotting
Anticlotting factors proteins made by the body that, when activated, inhibit blood from clotting
Clotting factors proteins made by the body that, when activated, cause blood to clot.
FDA Food and Drug Administration- a branch of the federal government regulating the licensing and use of medications in the United States.
Thrombolytic a substance that dissolves existing blood clots


Other Sites & Resources



Doctors Corner INternet Group, Inc. 1997-2004