Deep vein thrombosis (DVT) occurs when blood clots form in the deep veins of the legs. The condition can be painful and may result in blood clots breaking free and traveling to the lungs (embolism), where they may obstruct blood flow and cause serious health problems or death.
DVT occurs most often among people over the age of 50. In recent years, researchers have identified a number of risk factors that may contribute to DVT. They include inherited conditions, long periods of immobility, pregnancy, recent surgery or trauma to the legs, smoking, cancer, use of birth control pills and certain forms of heart disease.
Once diagnosed, deep vein thrombosis is usually treated with medication that helps prevent additional blood clots from forming or existing blood clots from growing larger. Physicians may also prescribe special compression stockings that help blood flow upward through the veins of the leg. In serious cases, a device called a vena cava filter may be implanted into the veins of the leg. This basket–like device prevents blood clots from traveling up into the lungs.
Deep vein thrombosis is a type of thrombophlebitis. However, it should not be confused with a less dangerous form of thrombophlebitis called superficial vein thrombosis (SVT or phlebitis). SVT occurs when blood clots form in the surface veins of the legs. This condition is not as dangerous because these blood clots will not travel to the lungs.
About deep vein thrombosis (DVT)
Deep vein thrombosis (DVT) occurs when blood clots form in the deep veins of the legs, including veins in the calves, thigh or hip. These veins are responsible for draining oxygen-poor blood from the lower extremities. After traveling up through the legs, they feed into a large vein called the inferior vena cava that connects to the right atrium. From there, the oxygen-poor blood drains into the right ventricle and is pumped into the pulmonary arteries. The pulmonary arteries are connected to the lungs, where the oxygen-poor blood sheds its waste products and picks up new oxygen.
About half of people who have deep vein thrombosis have no symptoms, while the other half may experience pain, throbbing or warmth in their legs. The condition is dangerous because of the risk that a blood clot will dislodge and travel to the lungs as an embolus. If it lodges in the lungs and restricts blood flow, it will result in a pulmonary embolism, a dangerous condition that can be fatal. The likelihood of a pulmonary embolism is somewhat related to the location of the DVT. DVT that is located in the calves is less likely to result in a pulmonary embolism than DVT that is located in the veins of the thighs or upper legs.
Deep vein thrombosis is more common among women and people over the age of 50, although it may occur among men and younger people as well. Researchers have identified a number of risk factors for deep vein thrombosis and estimate that as many as 80 percent of patients with DVT exhibit one or more risk factors. These risk factors include:
Long periods of immobility, surgery or recent trauma to the legs
Hormone replacement therapy (HRT)
Certain heart conditions (e.g., heart failure)
In recent years, the use of central venous catheters has also been connected to DVT. Roughly 10 percent of DVT cases have been attributed to these devices.
In the past, DVT thrombosis had been closely associated with airline travel (the so-called “economy class syndrome”) but recently researchers have begun to question the connection between airline travel and DVT. Because the risk of DVT increases with long periods of immobility, it may be that sitting in any seat for a long period of time may be the culprit behind the increased risk of DVT.
The risk of DVT is especially high among people who have experienced previous blood clots, including another form of thrombophlebitis called superficial vein thrombosis (SVT or phlebitis). In these conditions, blood clots form on the surface veins of the legs, but there is no risk they will travel to the lungs and cause pulmonary embolism. However, there is a possibility that one of these conditions will progress to DVT.
Therapy for DVT is aimed at preventing pulmonary embolism and relieving any symptoms that may be present. Physicians may choose to use medications, compression stockings or special filters that are implanted into the veins to catch loose blood clots before they can travel to the lungs.
Risk factors and causes for DVT
Physicians have identified a number of risk factors for deep vein thrombosis (DVT). As many as 80 percent of patients have one or more risk factors, and the risk factors tend to cluster in older people, which may help explain why DVT is more common among people over the age of 50. These risk factors include:
Inherited blood conditions (inherited thrombophilia). There are a number of genetic defects that are associated with an increased risk of venous blood clots. These account for many of the cases of DVT that occur in people under the age of 50. In general, these inherited conditions affect the ability of the blood to clot.
Venous malformations present at birth (congenital venous malformations). Infants born with an abnormal or absent inferior vena cava, which drains blood from the lower extremities, are at increased risk of recurrent episodes of DVT. Also, abnormalities of other veins, including the iliac, which runs inside the thigh, are associated with increased risk of DVT.
Cancer. Patients with cancer are sometimes “hypercoagulable,” meaning their blood clots more easily than others because of blood substances produced as a result of their disease. About 20 percent of patients with symptomatic DVT also have a malignancy, with lung cancer as the most common.
Surgery. The risk of DVT is increased greatly during surgeries including orthopedic, vascular and neurosurgery. The risk level raises when the patient is over age 40, has experienced previous blood clots, has cancer or heart disease, and is confined to a hospital bed for a long period of time. These individuals remain at risk for several days after hospital discharge. Preventive therapy is often recommended to prevent blood clots from traveling to the lungs and causing a possibly fatal pulmonary embolism.
Trauma. All forms of major injury are associated with an increased risk of blood clots and DVT. The reasons are not completely understood, but it may be connected to decreased blood flow to the extremities, immobilization and the depletion of natural anticoagulants, which prevent the blood from clotting, as a result of injury.
Pregnancy. The risk of DVT is raised during pregnancy, possibly as a result of the enlarged uterus obstructing venous blood flow from the legs and hips.
Birth control pills. The use of birth control pills is the leading cause of DVT among young women. Research has shown that the risk of DVT increases within four months of beginning birth control pills and decreases to previous levels within three months of stopping birth control pills.
Hormone replacement therapy. The use of hormone replacement therapy to treat the symptoms of menopause is associated with an increased risk of venous blood clots, including DVT. Hormone replacement therapy usually consists of an estrogen and synthetic progesterone combination.
Immobilization. Prolonged bed-rest or other forms of immobilization are associated with increased risk of DVT.
Travel. At one time, DVT was nicknamed the “economy class syndrome” because of the perception that frequent travel was a risk for DVT. Recent studies, however, have complicated the idea that airline travel alone can raise the risk for DVT. Instead, researchers speculate that the forced immobility of sitting in airline seats is a leading risk factor. Other studies, however, have linked the increase in DVT among airline travelers to dehydration, pressure changes within the airplane as it rises and descends, and the presence of other risk factors.
Heart failure. A condition characterized by the heart’s inability to pump enough blood to meet the oxygen needs of the body. In particular, left ventricle malfunction and atrial fibrillation are associated with DVT.
Seasonal change. Hospitalizations for DVT tend to increase during cold winter months, possibly because of reduced activity during the cold season or vasoconstriction as a result of cold.
Cardiovascular risk factors. There is an overlap between some risk factors for heart disease and risk factors for DVT, including elevated homocysteine obesity and diabetes.
Central venous catheters. The use of central venous catheters is associated with increased risk for DVT, especially among younger patients. These catheters are long, thin tubes that are placed into veins during surgery to administer medications and withdraw fluids.
Previous episodes of venous blood clots. The presence of previous blood clots in the veins is a major risk factor for DVT. Similarly, patients who have experienced pulmonary embolism because of DVT are much more likely to have recurrent episodes of pulmonary embolism.
Signs and symptoms of DVT
About half of patients with deep vein thrombosis (DVT) do not experience any symptoms. In others, symptoms include:
Swelling of the leg
Pain or tenderness in the leg that may only be present when standing or walking
Increased warmth in the leg that is swollen or hurts
Red or discolored skin
It is important for people experiencing these symptoms to see a physician. The location of the symptoms does not necessarily pinpoint the location of the blood clot.
Moreover, only about a third of people experiencing patients typical of DVT are actually suffering from the condition. In others, their symptoms are caused by other conditions, including muscle pulls and tears.
In many cases, people do not experience symptoms until a blood clot or piece of blood clot dislodges and travels to the lung, where it obstructs blood flow and causes a pulmonary embolism. It is estimated that about 90 percent of cases of pulmonary embolism are caused by DVT. Acute pulmonary embolism is a very dangerous condition that may result in death. Symptoms of pulmonary embolism include chest pain during deep breath and shortness of breath.
Diagnosis methods for DVT
Studies have shown that most patients with leg pain who visit a physician do not have deep vein thrombosis (DVT). Since the standard treatment for DVT (e.g., anticoagulants) can be dangerous for people who don’t need it, it is very important that the diagnosis be confirmed before therapy is begun.
The diagnosis of deep vein thrombosis begins with a thorough physical examination. The examination may reveal a “cord” running through the leg, so the physician will massage and feel closely along the entire length of the leg. A thorough medical history is also important. Up to 80 percent of patients with DVT have one or more known risk factors (e.g., inherited blood disorders, long periods of immobility, pregnancy, cancer, surgery).
If the physician still suspects DVT, tests may be performed, including:
Duplex ultrasound. This noninvasive, common test uses sound waves to visualize the veins of the leg. Test results are displayed on a computer screen so the physician can look for obstructions. It is the most common test used to diagnose DVT, especially first episodes.
Impedance plethysmography. During this noninvasive test, a blood pressure cuff is inflated around the thigh, restricting blood flow, while the change in blood volume is measured at the calf with electrodes. The blood pressure cuff at the thigh is rapidly deflated so the physician can measure the rate at which the blood flows from the calf and compare this rate to another, healthy limb. This test is particularly helpful to diagnose recurrent episodes of DVT. However, use of the test is limited because it takes a high degree of training to administer it accurately.
Contrast venography. This invasive test is considered the “gold standard” for detecting DVT. During this test, a contrast medium is injected into the veins that helps the physician see any obstructions. Although this is the most accurate test, it is used less often than ultrasound because it is invasive and may be uncomfortable for the patient. Currently, contrast venography is recommended if ultrasound or impedance plethysmography are unavailable or if the patient cannot withstand them (e.g. because of a cast on a limb).
Studies have also found that test accuracy is increased if physicians first measure the “pretest probability” of a patient having DVT. The most commonly used method to measure pretest probability is to measure a blood substance called D-dimer, a product of fibrin degradation that is elevated among patients with thromboembolism conditions, including DVT. During this standard blood test, blood will be withdrawn, either from the arm or by finger-prick, and sent to a laboratory for analysis.
An elevated D-dimer is not enough to diagnose DVT, but it is enough to warrant further testing. Studies have shown that less than 10 percent of people who had D-dimer levels less than 500 ng/mL were later diagnosed with thromboembolism conditions, including DVT. D-dimer levels may also be elevated because of cancer, recent trauma or surgery.
Finally, physicians are beginning to use two additional tests to diagnose DVT, although both still remain relatively rare. They are:
Magnetic resonance imaging (MRI). This noninvasive test uses radio waves to visualize the structures inside the body. It may or may not require contrast material (magnetic resonance venography).
Computed axial tomography scan (CAT scan). This noninvasive test uses an array of x-ray scanners to create three-dimensional images of internal structures on a computer screen. It is only rarely used to diagnose DVT and its use is currently considered experimental.
Treatment and prevention of DVT
Treatment for deep vein thrombosis (DVT) is designed to stop existing blood clots from getting bigger, preventing blood clots from breaking off and traveling to the lungs (pulmonary embolism), and reducing the likelihood of another blood clot forming.
The first line of treatment is usually medication, including:
Anticoagulants. These medications decrease the blood’s ability to clot. They are used in patients who experience symptoms to prevent clots from enlarging or to stop new clots from forming. They do not break up existing clots. Depending on the severity of the DVT, anticoagulant therapy may begin immediately after diagnosis and continue for several months (usually 3 to 6 months). If the patient has other conditions that may contribute to the DVT (e.g. cancer), anticoagulant therapy will often last as long as those other conditions are present. Anticoagulant medications may be administered in the hospital (e.g., heparin), followed by an oral prescription (e.g., warfarin). It is very important to closely monitor anticoagulant medications, using the international normalized ratio (INR), closely while they are being used to reduce the risk of bleeding. Newer forms of heparin have been studied that allow for safe treatment of DVT without hospitalization.
Clot-busting drugs (thrombolytics). These medications dissolve existing blood clots. They are frequently used among stroke patients to rapidly dissolve blood clots that occur in the brain. However, in DVT their use is somewhat controversial, since anticoagulant therapy is effective and thrombolytics are connected to increased bleeding and many DVT patients also recently had surgery, which would prohibit the use of clot-busting drugs. Their use is usually reserved for severely symptomatic blood clots that are life-threatening.
Thrombin inhibitors. These are newer medications that interfere with the blood’s clotting process. They are often used with patients who cannot tolerate anticoagulation.
If a patient cannot tolerate medications for one reason or another, the physician may choose to implant a vena cava filter. This is a basket-like filter that is placed into the large vein that drains the legs and lower extremities, the inferior vena cava. The filter is designed to prevent loose blood clots from reaching the lungs and causing a pulmonary embolism.
Finally, the physician may prescribe graduated compression stockings. These stockings are worn from the foot to the just above or below the knee. They are tight at the ankle and gradually provide less pressure as they move up the leg. This aids upward blood circulation and reduces swelling in the legs that results from damage to the valves in the veins.
It is very important that compression stockings be worn according to the physician’s instructions. Despite the fact they can be hot and sometimes difficult to put on, studies have shown that poor compliance rates with the stockings hinders their effectiveness. Newer stockings are available that use Velcro fasteners.
Besides these therapies, a physician may also recommend reducing the number of risk factors for DVT. This may include walking regularly to get exercise and stimulate circulation, avoiding activities that may cause serious injury to the legs and diet modification.
Questions for your doctor
Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions related to deep vein thrombosis:
What can I do to prevent deep vein thrombosis?
How do I know if my leg pain is something I should worry about?
Do I have any of the risk factors commonly associated with deep vein thrombosis?
Does deep vein thrombosis pose a significant danger to my health?
What type of tests can I take to allow you to better evaluate my condition?
Could I still have deep vein thrombosis is I don't feel any pain in my legs?
What types of therapies are available to me for the treatment of deep vein thrombosis?
Are there any lifestyle changes I can make that may decrease my chances of developing deep vein thrombosis?
What should I do if I experience pain or swelling in my legs?
Does being pregnant put me at increased risk for deep vein thrombosis?
