Deep venous thrombosis is a blood clot that forms in a vein deep inside a part of the body. It mainly affects the large veins in the lower leg and thigh.
DVTs are most common in adults over age 60. But, they can occur at any age. When a clot breaks off and moves through the bloodstream, this is called an embolism. An embolism can get stuck in the brain, lungs, heart, or other area, leading to severe damage.
Blood clots may form when something slows or changes the flow of blood in the veins. Risk factors include:
- A pacemaker catheter that has been passed through the vein in the groin
- Bed rest or sitting in one position for too long such as plane travel
- Family history of blood clots
- Fractures in the pelvis or legs
- Giving birth within the last 6 months
- Recent surgery (most commonly hip, knee, or female pelvic surgery)
- Too many blood cells being made by the bone marrow, causing the blood to be thicker than normal
Blood is more likely to clot in someone who has certain problems or disorders, such as:
- Certain autoimmune disorders, such as lupus
- Cigarette smoking
- Conditions that make it more likely to develop blood clots
- Taking estrogens or birth control pills (this risk is even higher with smoking)
Sitting for long periods when traveling can increase the risk of DVTs. This is most likely when you also have one or more of the risk factors listed above.
DVT mainly affects the large veins in the lower leg and thigh, almost always on one side of the body. The clot can block blood flow and cause:
- Changes in skin color (redness)
- Leg pain
- Leg swelling (edema)
- Skin that feels warm to the touch
Exams and Tests
Your health care provider will perform a physical exam. The exam may show a red, swollen, or tender leg.
The two tests that are often done first to diagnose a DVT are:
- D-dimer blood test
- Doppler ultrasound exam of the legs
Blood tests may be done to check if you have an increased chance of blood clotting, including:
- Activated protein C resistance (checks for the Factor V Leiden mutation)
- Antithrombin levels
- Antiphospholipid antibodies
- Complete blood count (CBC)
- Genetic testing to look for mutations that make you more likely to develop blood clots, such as the prothrombin G20210A mutation
- Lupus anticoagulant
- Protein C and protein S levels
Your doctor will give you medicine to thin your blood (called an anticoagulant). This will keep more clots from forming or old ones from getting bigger.
Heparin is usually the first drug you will receive.
- If heparin is given through a vein (IV), you must stay in the hospital.
- Newer forms of heparin can be given by injection under your skin once or twice a day. You may not need to stay in the hospital as long, or at all, if you are prescribed this newer form of heparin.
Depending on your medical history, fondaparinux may be recommended by your doctor as an alternative to heparin.
A blood-thinning drug, for example warfarin (Coumadin), is usually started along with heparin.
- Warfarin is taken by mouth. It takes several days to fully work.
- Heparin is not stopped until the warfarin has been at the right dose for at least 2 days.
- You will most likely take warfarin for at least 3 months. Some people must take it longer, or even for the rest of their lives, depending on their risk for another clot.
When you are taking warfarin, you are more likely to bleed, even from activities you have always done. If you are taking warfarin at home:
- Take the medicine just the way your doctor prescribed it.
- Ask the doctor what to do if you miss a dose.
- Get blood tests as advised by your doctor to make sure you are taking the right dose.
- Learn how to take other medicines and when to eat.
- Find out how to watch for problems caused by the drug.
You will be given a pressure stocking to wear on your leg or legs. A pressure stocking improves blood flow in your legs and reduces your risk for complications from blood clots. It is important to wear it every day.
In rare cases, you may need surgery if medicines do not work. Surgery may involve:
- Placing a filter in the body's largest vein to prevent blood clots from traveling to the lungs
- Removing a large blood clot from the vein or injecting clot-busting medicines
Many DVTs disappear without a problem, but they can return. Some people may have long-term pain and swelling in the leg called post-phlebitic syndrome.
You may also have pain and changes in skin color. These symptoms can appear right away or you may not develop them for 1 or more years afterward. Wearing tight (compression) stockings during and after the DVT may help prevent this problem.
Blood clots in the thigh are more likely to break off and travel to the lungs (pulmonary embolus, or PE) than blood clots in the lower leg or other parts of the body.
When to Contact a Medical Professional
To prevent deep vein thrombosis:
- Wear the pressure stockings your doctor prescribed.
- Moving your legs often during long plane trips, car trips, and other situations in which you are sitting or lying down for long periods.
- Take blood thinning medicines your doctor prescribes.
- Do not smoke. Talk to your doctor if you need help quitting.
DVT; Blood clot in the legs; Thromboembolism; Post-phlebitic syndrome; Post-thrombotic syndrome
Dupras D, Bluhm J, Felty C, et al. Institute for Clinical Systems Improvement. Venous thromboembolism diagnosis and treatment. Updated January 2013. Accessed March 24, 2014.
Ginsberg J. Peripheral venous disease. In: Goldman L, Schafer AI, eds.Cecil Medicine
Guyatt GH, Akl EA, Crowther M, et al. Executive Summary: Antithrombotic Therapy and Prevention of Thrombosis. 9th ed. American College of Chest Physicians Evidence-Based Clinical Practice Guidelines. Chest
Update Date 2/24/2014
Updated by: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.