Deep Vein Thrombosis (Blood Clot in the Leg, DVT)
Exams and Tests
There is no blood test for deep vein thrombosis. After a physical exam, the doctor might do some of these tests:
- Doppler ultrasound: This test uses high-frequency sound waves to show the large veins in the leg and a blood clot. Painless and without complications, this is the most commonly used test to diagnose deep vein thrombosis. But sometimes the test can miss a clot, especially in the smaller veins.
- Venography: A liquid dye is injected into the veins. It highlights blockage of blood flow by a clot on an image of the legs. 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 changes in blood volume within veins. Because this test does not find 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 DVT as it is more difficult to interpret and is time consuming. The CT scan is more useful for finding blood clots in the lung.
Deep Vein Thrombosis Treatment
DVT is usually treated with blood-thinning medication prevent more clots and to prevent the clot from traveling to the lung and causing a pulmonary embolism:
- Warfarin (Coumadin) is a pill that thins the blood. It may take a few days to work. The dose is different for each person, and blood clotting must be checked often since diet, activity, and other drugs can affect warfarin.
- Enoxaparin (Lovenox) is a drug injected under the skin to thin the blood. Enoxaparin usually is only used for a short time, but it may be used over the long term in some patients with cancer.
- Rivaroxaban (Xarelto) is also a pill. In studies on preventing deep vein thrombosis and pulmonary embolism, Xarelto was as effective as another treatment combining Lovenox and warfarin
How long someone takes blood thinners depends on how the clot developed. 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.
Sometimes the doctor will inject clot-dissolving drugs called thombolytics directly into a clot. This has a higher chance of complications than using blood-thinning drugs.
Not all DVTs require blood thinners. Because small clots located in veins below the knee have a low risk of traveling to the lung, people with them may only be watched by the doctor. Using ultrasound tests of the veins, the clot can be monitored to see whether it is growing.