Overview
Deep venous thrombosis (DVT) refers to a blood clot embedded in one of the major deep veins of the lower legs, thighs, or pelvis. A clot blocks blood circulation through these veins, which carries blood from the lower body back to the heart. The blockage can cause pain, swelling, or warmth in the affected leg. Blood clots in the veins can cause inflammation (irritation) called thrombophlebitis. Severe complications of deep vein thrombosis occur when a clot breaks loose (or embolizes) and travels through the bloodstream, causing blockage of blood vessels (pulmonary arteries) in the lung. Called pulmonary embolism, this can lead to severe difficulty in breathing and even death, depending on the degree of blockage.
Causes
Three factors may lead to formation of a clot inside a blood vessel.

• Damage to the inside of a blood vessel due to trauma or other conditions
• Changes in normal blood flow, including unusual turbulence, or partial or complete blockage of blood flow
• Hypercoagulability, a rare state in which the blood is more likely than usual to clot

Any component that contributes to one or more of these three criteria can cause deep vein thrombosis. The more common risk factors are as follows:

• Prolonged sitting, such as during a long plane or car ride
• Prolonged bed rest or immobility, such as after injury or during illness (such as stroke)
• Recent surgery, particularly orthopedic, gynecologic, or heart surgery
• Recent trauma to the lower body, such as fractures of the bones of the hip, thigh, or lower leg
• Obesity
• Heart attack or heart failure
• Recent childbirth
• Being at very high altitude, greater than 14,000 feet
• Use of estrogen replacement (hormone therapy, or HT) or birth control pills
• Cancer
• Rare inherited genetic changes in certain blood clotting factors
• Disseminated intravascular coagulation (DIC), a medical condition in which blood clotting occurs inappropriately, usually caused by overwhelming infection or organ failure
• Certain heart or respiratory conditions
• Advanced age

If an individual has one deep vein thrombosis, they are more likely to have a second deep vein thrombosis.

Symptoms
Symptoms occur in the affected leg when a clot obstructs blood flow and causes inflammation. Symptoms may include the following:

• Swelling
• Gradual onset of pain
• Redness
• Warmth to the touch
• Worsening leg pain when bending the foot
• Leg cramps, especially at night
• Bluish or whitish discoloration of skin

However, almost 30%-50% of individuals with deep vein thrombosis do not experience symptoms from the condition.

Exams and Tests
Upon hearing the patient's symptoms, the health care practitioner may suspect that the patient has a deep vein thrombosis, especially if they have any of the risk factors.
No accurate blood test is available to diagnose deep vein thrombosis. Therefore, a variety of imaging tests are used to confirm the diagnosis.

• Doppler ultrasound: Using high-frequency sound waves, this system can visualize the large, proximal veins and detects a clot if one is present. Painless and without complications, this is the most commonly used method to diagnose deep vein thrombosis. However, sometimes the test can miss a clot, especially in the smaller veins.
• Venography: A liquid dye is injected into the veins for imaging studies. It highlights blockage of blood flow by a clot. This is the most accurate test, but also the most uncomfortable and invasive. It is rarely done today because of the availability of better ultrasound machines.
• Impedance plethysmography: Electrodes are used to measure volume changes within veins. Because this test does not detect clots better than ultrasound and is harder to perform, it is rarely used.

CT scan: This is a type of X-ray that gives a very detailed look at the leg veins in cross section and can detect clots. It is rarely used for this purpose.
Treatment
Medical Treatment
The treatment of blood clots depends upon their location in the body. Most commonly, though, anticoagulation or blood thinning medication is prescribed to prevent further clot formation and to minimize the risk that part of the blood clot will break off and travel to the lung and cause pulmonary embolism.
Treatment of deep venous thrombosis in the leg is often individualized for each patient depending upon the clinical situation and other medical conditions that may be present.
Anticoagulation is the treatment of choice and is a two stage process. Low molecular weight heparin (enoxaparin ,dalteparin injections are started to begin immediate blood thinning. At the same time, warfarin (Coumadin) is prescribed (an oral anticoagulation medication that takes a few days to become effective and adequately anti-coagulate the blood). Blood tests (prothrombin time or international normalized ratio [INR]) are used to measure the effectiveness of the warfarin therapy. When the INR reaches the appropriate level, the heparin injections are discontinued.
If possible, the treatment of uncomplicated deep venous thrombosis in an individual is accomplished as an outpatient. Education is provided to the patient and family to teach them how to administer the injection, and the patient is instructed to return to their family physician or the hospital for appropriate monitoring (blood tests). Some patients will need to be admitted to hospital if they have significant underlying medical illnesses, are pregnant, or are unable to administer the heparin injections.
The duration of anticoagulation therapy depends upon the circumstances that led to the development of the blood clot. If there were temporary risk factors, for example a long trip or recent immobility because of injury or illness, treatment may last 3-6 months. However, if the cause is unknown or it there is recurrent clot, medication may be required for more than 12 months.
Not all DVTs require anticoagulation. Because small clots located in veins below the knee have a low risk of embolizing to the lung, it is possible to observe the patient. Using serial ultrasound tests of the veins, the clot can be monitored to see whether it is extending and growing or whether it is stable and needs no further treatment.
Blood clots located in the femoral vein near the groin that extend into the iliac vein in the abdomen may require more aggressive treatment with thrombolytic (thrombo=clot + lysis=breakdown) therapy. Clot-busting drugs (alteplase, streptokinase) may be injected directly into the clot itself. This usually requires a specialist who can use fluoroscopy or real time X-rays to position a catheter or tube into the affected vein where the clot resides and drips the medication in over a period of time to dissolve the clot and prevent it from traveling to the lung.
Similar situations can exist in the arm. DVTs above the elbow are usually treated with blood thinner medications as described above, while clots in the subclavian vein, located just below the collarbone, may be considered for thrombolytic therapy.
Because of underlying medical conditions, some people may not be able to take anticoagulation medications and may require an alternative treatment instead of medication. Those who have gastrointestinal bleeding (bleeding from the stomach or bowel), intracranial bleeding (bleeding in the brain), or who have had recent major trauma potentially could bleed to death if anticoagulation medications are prescribed. The alternative for leg DVT treatment in these situations may be an inferior vena cava filter. The vena cava is the large vein that collects blood from the lower body just before it enters the heart. A filter can be placed into the vena cava to trap any clots that might break off and prevent them from traveling to the heart and then to the lungs.
Compression stockings are useful in preventing a complication of a leg blood clot called post thrombotic syndrome or post phlebitis syndrome, in which the affected leg swells and becomes chronically painful. These stockings may be purchased over-the-counter or can be custom fitted. It is recommended that they be worn for at least a year after the diagnosis of deep venous thrombosis.

• More difficult to interpret and is time consuming. The CT scan is more useful for identification of blood clots in the lung.

Medications
Warfarin (Coumadin) is an oral medication taken to thin or anti-coagulate the blood. It may take a few days for its action to take effect. The dose needs to be individualized for each person, and blood clotting must monitored routinely since changes in diet, activity, and the administration of other medications may affect the levels of warfarin. Blood tests (usually INR, or international normalized ratio) are done routinely to monitor the blood thinning effects and help the health care practitioner select the appropriate warfarin dose. Ideally, the INR should be kept in a range between 2.0 and 3.0. Blood tests are done weekly until the INR stabilizes and then are done every two weeks to every month.
Enoxaparin is a low molecular weight heparin injected beneath the skin to thin the blood. The dose is usually 1milligram per kilogram of weight injected twice daily or 1.5 milligrams per kilogram injected once daily. Enoxaparin usually is considered a temporary medication to be used to thin the blood while warfarin begins to take effect; however, it may be used over the long-term in some patients with cancer.
Surgery
Surgery is a rare option in treating large deep venous thrombosis of the leg in patients who cannot take blood thinners or who have developed recurrent blood clots while on anti-coagulant medications. The surgery is usually accompanied by placing an IVC (inferior vena cava) filter to prevent future clots from embolizing to the lung.
Phlegmasia Cerulea Dolens describes a situation in which a blood clot forms in the iliac vein of the pelvis and the femoral vein of the leg, obstructing almost all blood return and compromising blood supply to the leg. In this case surgery may be considered to remove the clot, but the patient will also require anti-coagulant medications.

 Follow-up
A person who has had a deep vein thrombosis may be asked to return for follow-up Doppler ultrasounds or other imaging studies if the leg swelling persists of if the symptoms recur. During anticoagulant treatment, it is often advised to take the following measures:

• Take the prescribed amount of medication. Do not miss or add doses.
• Follow the health care practitioner's instructions closely about when to get lab tests for blood coagulation.
• Ask the health care practitioner before starting or stopping any medication, including over-the-counter medications. Many medicines increase or otherwise interfere with the effect of anticoagulants.
• Ask what foods should be avoided, because some foods may change the effectiveness of blood-thinning drugs.
• Wear a Medic-alert bracelet with information about any anticoagulants that you are taking.
• Inform any other medical professionals including dentists or podiatrists that you are taking an anticoagulant before undergoing any procedure.

 
Prevention
The key to prevention is to reverse any risk factors, for example:

• If a person is obese, lose weight.
• Avoid periods of prolonged immobility.
• Keep the legs elevated while sitting down or in bed.
• Avoid high-dose estrogen pills, unless they are deemed necessary by the health care practitioner.

If you have had surgery recently, preventive treatment may be prescribed to avoid formation of a clot.

• You may be instructed to get out of bed several times a day during the recovery period.
• Sequential compression devices (SCDs) may be placed on the legs. Their squeezing action has been shown to reduce the probability of clot formation. You also may be given elastic stockings to wear.

Low molecular weight heparin or low-dose warfarin may be prescribed to prevent clot formation.
Outlook
Most DVTs resolve on their own.

• However, nearly 20% of untreated DVTs located above the calf embolize to the lung (pulmonary embolus), and 10%-20% of those are fatal.
• More than 90% of life-threatening pulmonary emboli arise from DVTs in the legs.

If an individual has had one deep vein thrombosis, they are more likely than the average person to have another deep vein thrombosis.

• A second deep vein thrombosis occurs within three months in 5% to 8% of people who have had one deep vein thrombosis and within two years in 20%. By some estimates, approximately 50% of those who have had deep vein thrombosis will suffer a recurrence.
• Closely follow the prevention instructions from the health care practitioner.

Anticoagulant therapy lowers the death rate from pulmonary embolism by a 5 to 10 fold factor.