Blood Clots: Deep Vein Thrombosis Diagnosis

  • Diagnosis

    Deep vein thrombosis (DVT) is a blood clot in a deep vein of the body, usually in the thigh or leg. The deep veins are the main blood vessels returning blood from the tissues of the body back to the heart (such as the femoral vein). Figure 01.

    Click to enlarge: Deep vein thrombosis

    Figure 01. Deep vein thrombosis

    If a blood clot (thrombus) forms in a deep vein, it can block the flow of blood, which prevents the tissues from draining properly. This causing excess fluid accumulation, swelling, warmth, and discomfort in the leg. A blood clot in a deep vein may also break off and travel back to the heart and into the lungs, causing a condition called pulmonary embolism. Pulmonary embolism can be minor and go unnoticed, or it can be significant and cause difficulty breathing, sharp chest pain, and even death. Less commonly, the clots can also travel through the heart back to the rest of the body, including the brain. This is called a paradoxic embolism. A blood clot that travels this way to the brain can be a cause of stroke.

    DVT is different from a clot in a vein close to the surface of the body, such as a vein near the skin or in the calf. These superficial clots, while often uncomfortable, are usually not dangerous and are not treated in the same way as DVT.

    DVT is treated with medications that lower the chances of new clots forming and allow the body to dissolve the clot over time.

    Blood clots in the veins of the legs cause DVT. When the bloodflow in the arteries and veins is blocked, a blood clot (thrombus) may form. A thrombus that forms in the larger veins of the legs may break off and travel through the bloodstream to become an embolus.

    People who have conditions that cause blood to flow slowly in the veins, or who have a higher chance of blood clots, are at greatest risk of developing DVT.

    The condition tends to occur in people who:

    • Have had a previous DVT
    • Are inactive
    • Have damaged blood vessels due to injury or surgery to legs or hips
    • Have blood that clots more easily, such as in some diseases and genetic conditions
    • Are in the hospital on bedrest, such as after a hip operation or other major surgery, or during a major illness.

    Symptoms of DVT usually occur in one leg. Pain, warmth, and swelling are just some of the symptoms. Other symptoms include tenderness, discomfort, changes in skin color (e.g. bluish skin discoloration or redness), and joint pain.

    The pain often is below the knee--often in the calf--and may increase during standing or walking. However, many people with DVT may not show symptoms. If pulmonary embolism occurs, symptoms include shortness of breath and sharp chest pain that is worse with taking a deep breath.

    Lack of exercise or movement may predispose people to DVT. People who do not move for prolonged periods of time, such as during a long plane flight or a cross-country drive, are at risk for DVT. It is important to change positions often; stand up and walk around at least once every one to two hours. You can also flex your feet and leg muscles while sitting.

    Most often, DVT forms when a person is hospitalized and at bedrest, such as after a hip operation or for another major illness or surgery. Ten percent to thirty percent of medical and surgical intensive care unit patients have DVT within the first week of admission. As a result, patients who are subject to bed rest should follow an exercise routine that uses active and passive motion of the arms and legs.

    If you cannot exercise your legs, your doctor may recommend special treatments to lower the risk of DVT, such as compression stockings or medications.

    A traumatic injury or surgery--especially to the legs or hips--may predispose people to DVT. This risk can occur as a result of trauma to the blood vessels, or as a result of the long period of immobilization required after a major surgery or an injury such as a fracture.

    Pregnancy and certain hormonal medications may predispose women to DVT. During pregnancy and for three months following childbirth, women are at increased risk for DVT. Medications such as estrogen and birth control pills may cause women to be at increased risk of DVT, especially in women who are also smokers.

    Obesity may predispose people to DVT Figure 02

    Click to enlarge: BMI calculator

    Figure 02. BMI calculator

    People who are obese may have other conditions that increase the risk of DVT. In addition, a large number of obese people are less active, which may also increase the risk of blood clots.

    Certain inherited conditions may predispose people to DVT. In order for blood clots to form and dissolve, certain factors in the blood are necessary. Some inherited conditions cause defects in these factors; individuals with these defects are more likely to form blood clots. The most common defect is resistance to a protein called activated protein C (factor V Leiden); people with this defect are more likely to form a DVT.

    People with certain cancers such as lung or breast cancer may be at increased risk for developing DVT.

    Elderly people may be predisposed to DVT. As the condition of the heart and veins changes with age, DVT becomes more common. The blood vessels become thicker, stiffer, and less elastic. Circulation may slow and blood clots may result.

    If you are suspected of having DVT, you may undergo several tests to evaluate your veins and the tendency of your blood to clot. Imaging tests may locate the blood clot and confirm a diagnosis of DVT. Doctors can also analyze your blood to determine if it is likely to form clots.

    • Duplex ultrasound. This is the most frequently used test for detecting DVT. This test uses sound waves to provide images of the veins of the thigh and calves, and is fairly accurate for detecting blood clots. This test turns sound waves into an image that can be viewed on a monitor.
    • Impedance plethysmography (IPG). This study enables your doctor to measure how your blood vessels conduct a weak electrical impulse. If you have DVT, the electrical charge that is measured is reduced due to the blockage caused by an embolus.
    • Magnetic resonance angiography (MRA). This test is sometimes used, but it is not commonly used for detecting DVT because it is expensive and not widely available.
    • Fibrinogen uptake radionuclide imaging. This test is most useful for detecting DVT in the thighs.
    • Radionuclear imaging. This test is relatively new and involves using a small amount of radioactive material to detect DVT above the knee or in the pelvic veins.
    • D-dimer. This blood test measures a substance that collects during the formation of a blood clot. Because many other conditions can change levels of this test, it is not always useful for determining that you do have a DVT. But if the level of D-dimer in your blood is zero or very low, it means you do not have a DVT.

    Invasive tests may be used to detect DVT.

    • Ascending contrast venography. Although this test is highly accurate for detecting DVT, it is not often used because of the risks, discomfort, and cost involved. After a contrast dye is injected into a foot vein, x-rays are taken of the leg and pelvis, and the doctor will be able to locate clots. Complications of ascending contrast venography include phlebitis, a painful inflammation of the superficial veins.
    • Contrast-enhanced spiral computed tomography. For this highly sensitive test, the doctor injects a dye into the vein in your foot, and you are placed in a scanner which takes x-ray pictures of your veins.

    Other tests may be used to rule out other possible causes of your symptoms.

    Move your legs if you sit for long periods of time. Prolonged sitting, bed rest, and lack of movement increase the chance of blood clots forming in the deep veins of the legs. When you have to sit for long periods of time--for example, during long airline flights--move your legs, such as by flexing your ankle up and down (as though you are pressing the accelerator of a car with your foot). Repeat this exercise 20 times every one to two hours.

    Walk up and down the aisle of a plane every hour or two for a few minutes. If traveling in a car, pull over at a rest stop to stretch your legs every two hours.

    Increase your intake of fluids when traveling in an airplane. People who travel in airplanes for extended periods of time have a tendency to become dehydrated. If you have a history of blood clots, dehydration may cause your blood to thicken, increasing your risk of developing DVT. To prevent dehydration, drink an eight-ounce glass of water every two hours. Avoid drinking too much alcohol and coffee when flying, as they increase dehydration.

    Wear elastic compression stockings. If you have a history of blood clots or leg swelling, elastic stockings reduce leg swelling and reduce the chance that blood clots will form in the legs. The stockings must be worn snugly in order to offer support while ensuring adequate circulation. Stockings should not be worn for more than a full day at a time. They are available over-the-counter at surgical supply stores. These elastic compression stockings work by periodically filling with air and squeezing your legs.

    Small doses of aspirin may decrease surgical complications associated with the formation of blood clots and DVT. Research suggests that aspirin may reduce the risk of blood clot formation in patients who have surgery for a hip fracture. Compared to other medications used to prevent blood clot formation, aspirin is easy to take and inexpensive. Some people cannot tolerate aspirin, so you should speak with your doctor before taking it regularly.

  • Prevention and Screening

    Move your legs if you sit for long periods of time. Prolonged sitting, bed rest, and lack of movement increase the chance of blood clots forming in the deep veins of the legs. When you have to sit for long periods of time--for example, during long airline flights--move your legs, such as by flexing your ankle up and down (as though you are pressing the accelerator of a car with your foot). Repeat this exercise 20 times every one to two hours.

    Walk up and down the aisle of a plane every hour or two for a few minutes. If traveling in a car, pull over at a rest stop to stretch your legs every two hours.

    Increase your intake of fluids when traveling in an airplane. People who travel in airplanes for extended periods of time have a tendency to become dehydrated. If you have a history of blood clots, dehydration may cause your blood to thicken, increasing your risk of developing DVT. To prevent dehydration, drink an eight-ounce glass of water every two hours. Avoid drinking too much alcohol and coffee when flying, as they increase dehydration.

    Wear elastic compression stockings. If you have a history of blood clots or leg swelling, elastic stockings reduce leg swelling and reduce the chance that blood clots will form in the legs. The stockings must be worn snugly in order to offer support while ensuring adequate circulation. Stockings should not be worn for more than a full day at a time. They are available over-the-counter at surgical supply stores. These elastic compression stockings work by periodically filling with air and squeezing your legs.

    Small doses of aspirin may decrease surgical complications associated with the formation of blood clots and DVT. Research suggests that aspirin may reduce the risk of blood clot formation in patients who have surgery for a hip fracture. Compared to other medications used to prevent blood clot formation, aspirin is easy to take and inexpensive. Some people cannot tolerate aspirin, so you should speak with your doctor before taking it regularly.

Recommended Reading

Meet the Pharmacists

I'm Beth Isaac, PharmD. Welcome to PDR Health!

Check out my latest post on cholesterol drugs.

Blood Clots: Deep Vein Thrombosis Related Drugs

Blood Clots: Deep Vein Thrombosis Related Conditions