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What is Thrombosis?

You have thrombosis [throm-BOH-sis] when you have a blood clot in your body. Another word for a blood clot is a thrombus. A blood clot can be superficial [soo-per-FISH-uhl] if it is near the surface of the skin. Sometimes a superficial clot will move deeper. Other times, a blood clot will form in the deep tissues, and that is called deep vein thrombosis (DVT). Most of the time, a DVT is a blood clot deep in the leg.

DVTs are dangerous. They can damage the valves in your veins, leading to chronic pain and swelling. They can also break loose and travel in your veins. A blood clot that has broken loose is called an embolism [EM-buh-liz-um]. If it has travelled to the lungs, it is called a pulmonary [PUHL-moh-ner-ee] embolism or PE. A PE can be life threatening.


Often deep vein thrombosis has no noticeable symptoms. If you do have symptoms, they can include:

  • Pain in the affected area (such as a leg)
  • Swelling in the affected area
  • Redness or warmth in the affected area

Sometimes the first noticeable symptoms are from a pulmonary embolism. These symptoms can include:

  • Shortness of breath that comes on suddenly
  • Chest pain that gets worse when you breathe deeply or cough
  • Coughing or vomiting blood

If you experience symptoms of pulmonary embolism, call 911 and get medical help immediately.

When to See a Doctor

You should seek medical help right away if you have symptoms of thrombosis, including deep vein thrombosis:

  • Pain or tenderness in one leg when walking or standing
  • Swelling in one calf, ankle, foot, or thigh
  • Redness or warmth in part of your leg

Call 911 if you have any of these signs of pulmonary embolism:

  • Shortness of breath that comes on suddenly
  • Chest pain that gets worse when you breathe deeply or cough
  • Coughing or vomiting blood


Blood clots can be caused by anything that slows or stops the flow of blood in your body. This can include inactivity, surgery, injury, or inherited factors. Risk factors include:

  • Sitting for a long time, such as when you are driving or flying
  • Long periods of bedrest, as when hospitalized or paralyzed
  • Injury to a deep vein from surgery, a broken bone, or other trauma
  • Birth control pills
  • Hormone replacement therapy
  • Cancer and some of its treatments
  • Heart failure
  • Pacemaker or catheter in a central vein
  • Being overweight or obese
  • Smoking
  • Personal or family history of DVT or embolism
  • Pregnancy and the first 6 weeks after giving birth

There are two main reasons you are at higher risk during pregnancy and the first 6 weeks after giving birth:

  • Hormones in your body make your blood more likely to clot than normal.
  • Slower blood flow (from your expanding uterus pressing on your blood vessels and from being less physically active) also promotes blood clotting.

Your risk of DVT is increased further if you’re on bed rest during pregnancy or recovering from a C-section (cesarean section) birth.

Diagnosis and Tests

If your doctor suspects you have DVT, you may be given one or more of these tests:

  • Ultrasound. Sound waves are used to measure the blood flow through your veins and to identify any blood clots.
  • Venogram. An x-ray is taken to produce an image of your veins and to identify blood clots.
  • CT or MRI scans. Computerized tomography (CT) and magnetic resonance imaging (MRI) provide images of the inside of the body, including the veins.
  • Blood tests. Your blood may be tested for an inherited blood clotting disorder. It may also be tested for a substance called D-dimer, which is usually present in patients with blood clots. If you don’t have it, your symptoms are probably not caused by a blood clot.


DVT needs to be treated right away. The goal of treatment for DVT is to prevent the blood clot from getting bigger or becoming an embolism (breaking off and traveling toward the lungs). Treatment also aims to keep you from getting more blood clots. Your treatment may include one or more of the following:

  • Self-care. Your doctor may recommend that you:
    • Elevate your leg.
    • Apply a heating pad for 20 minutes every 2 hours.
    • Limit your walking, physical work, and lifting.
  • Compression stockings. These can reduce the swelling that happens after a blood clot forms in your leg. The stockings are tighter near the ankle and looser near the top. This helps keep your blood from pooling and clotting.
  • Blood thinner medications. These medications (also called anticoagulants [an-tee-koh-AG-yuh-lunts]) reduce your blood's ability to clot. They can’t break up clots you already have, but they can prevent them from getting bigger. They can also prevent new clots from forming. They're usually taken for at least 3 months.
  • Clot busters. These medications (also called thrombolytics) are given to break up blood clots. Because they can cause severe bleeding, they're only given in very serious situations.
  • Filters. If you cannot take medications, you may have a small filter inserted into a large vein in the abdomen called the vena cava. If a blood clot breaks off, this will reduce the chance of it traveling to the lungs.


If you're at risk of having DVT or emboli, or have had one before, take these measures to help prevent having one in the future:

  • Have regular checkups with your doctor. Make sure your prescriptions are still correct.
  • Take all your medicine as prescribed.
  • If you’ve been in bed after surgery or an illness, get up and walk around as soon as possible.
  • If you have to sit for a long time, stand up and walk around every hour. Stretch your legs and feet every 20 minutes while sitting. Drink plenty of water.
  • Modify your lifestyle to improve your overall health. Maintain a healthy weight, quit smoking, and control your blood pressure.

If you are on bed rest or recovering from a C-section, your care team may suggest these preventive steps:

  • Sequential compression device (SCD). This device helps prevent DVT by gently squeezing your legs in sequence. This speeds circulation in your veins. Make sure your SCD is on your legs and that it is turned on for as long as you are confined to your bed. You may find the device noisy and perhaps a bit hot, but it’s important.
  • Medication. You may need to take an anticoagulant, a blood thinning medicine. It can help prevent clots from forming or getting bigger.

All pregnant women and women recovering from childbirth should follow these general measures for preventing DVT:

  • If you have to sit for a long time, stretch your legs and feet every 20 minutes. Get up and walk around every hour. (Note: This does not apply to women on bed rest.)
  • Drink plenty of water.
  • Follow your doctor’s or midwife’s advice about exercise and lifestyle changes such as quitting smoking.
  • Keep all of your scheduled visits with your doctor or midwife.
Thrombosis happens when you have a blood clot in your body. A blood clot can be superficial (near the surface of the skin). Sometimes a superficial clot will move deeper. Sometimes a blood clot will form in the deep tissues. Deep vein thrombosis (DVT) is a dangerous blood clot in the body’s deep tissues, usually in the leg. An embolism is a blood clot that has broken loose and can travel in your veins. If it reaches your lungs, it can be life threatening.