Health Library



What is thrombosis?

Thrombosis occurs when clots block blood vessels.

  • Venous thrombosis is when the blood clot blocks a vein. Veins carry blood from the body back into the heart.
  • Arterial thrombosis is when the blood clot blocks an artery. Arteries carry oxygenated blood away from the heart to the body.

What causes thrombosis?

Venous thrombosis may be the result of the following:

  • Disease or injury to the veins in the legs
  • Immobility for any reason
  • Fracture
  • Certain medications
  • Obesity
  • Inherited disorders or inherited predisposition
  • Autoimmune disorders that predispose to clotting
  • Medications, such as certain contraceptives, that increase the risk of clotting 

Varicose veins occur when blood pools and then clots in the legs. Clots in the legs may break loose and travel to the lungs. This can cause trouble breathing, pain, and in extreme cases, death.

Arterial thrombosis may be the result of arteriosclerosis. This is the hardening of the arteries where fatty or calcium deposits cause the arterial walls to thicken. This can lead to plaque instability and risk for rupture followed by thrombus.

When arterial thrombosis occurs in the coronary arteries (arteries that supply blood to the heart muscle), it can lead to a heart attack. When arterial thrombosis occurs in a blood vessel in the brain, it can lead to a stroke.

What are the risk factors for thrombosis?

Risk factors for arterial thrombosis may include:

  • Smoking
  • Diabetes
  • High blood pressure
  • High cholesterol
  • Lack of activity and obesity
  • Poor diet
  • Family history of arterial thrombosis 
  • Long periods of inactivity including surgery and long trips

What are the symptoms of thrombosis?

The following are the most common symptoms of thrombosis. However, each person may experience symptoms differently. Symptoms may include:

  • Pain isolated to one leg (usually the calf or inner thigh)
  • Swelling in the extremity
  • Chest pain
  • Numbness or weakness on one side of the body
  • Acute mental status changes 

The symptoms of thrombosis may look like other blood disorders or medical problems. Always consult your health care provider for a diagnosis.

How is thrombosis diagnosed?

In addition to a complete medical history and physical exam, other tests may include ultrasounds of the arteries and veins and blood tests including those to test how well blood clots.

Dye injection with angiography and catheterization may also be used, as well as MRI/MRA and CT. The diagnostic procedure advised depends on the type of thrombus and the location.

How is thrombosis treated?

Treatment may include:

  • Anticoagulant (blood thinning) medications, such as coumadin and heparin
  • Catheters (to expand the width of involved vessels)
  • Stent placement (a wire mesh scaffolding that holds open the blood vessel)
  • Medications, such as antiplatelets, tissue plasminogen activator (t-PA), and/or enzymes, such as streptokinase (to dissolve clots)

Other treatments may be advised by your health care provider.

What are the complications of thrombosis?

Thrombosis can block the blood flow in both veins and arteries. Complications depend on the site of the thrombosis. The most serious complications include stroke, heart attack, and serious breathing problems.

Can thrombosis be prevented?

Reducing the risk of thrombosis includes maintaining an active life-style, returning to activity as soon as possible after surgery, and exercising your legs during long trips. It is also important to quit smoking, lose weight, and manage other health conditions such as diabetes, high blood pressure, and high cholesterol.

Key points

  • Thrombosis occurs when clots obstruct or block veins or arteries.
  • Symptoms of thrombosis include pain and swelling in one leg, chest pain, or numbness on one side of the body.
  • Complications of thrombosis can be life-threatening, such as a stroke or heart attack.
  • Management of thrombosis includes medications that thin the blood or prevent clots, and stents or catheters to open blocked vessels.
  • Prevention includes being active, quitting smoking, losing weight, and managing other health conditions.

Next steps

Tips to help you get the most from a visit to your health care provider:

  • Before your visit, write down questions you want answered.
  • Bring someone with you to help you ask questions and remember what your provider tells you.
  • At the visit, write down the names of new medicines, treatments, or tests, and any new instructions your provider gives you.
  • If you have a follow-up appointment, write down the date, time, and purpose for that visit.
  • Know how you can contact your provider if you have questions.
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