Health Library Explorer
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A-Z Listings Contact Us
Click a letter to see a list of conditions beginning with that letter.
Click 'Topic Index' to return to the index for the current topic.
Click 'Library Index' to return to the listing of all topics.


What is thrombosis?

Thrombosis occurs when blood clots block your blood vessels. There are 2 main types of thrombosis:

  • 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 oxygen-rich blood away from the heart to the body.

What causes thrombosis?

Venous thrombosis may be caused by:

  • Disease or injury to the leg veins

  • Not being able to move around (immobility) for any reason

  • A broken bone (fracture)

  • Certain medicines

  • Obesity

  • Inherited disorders, or a greater likelihood of having a certain disorder based on your genes

  • Autoimmune disorders that make it more likely your blood will clot

  • Medicines that increase your risk of clotting(such as certain birth control medicines

Arterial thrombosis may be caused by a hardening of the arteries (atherosclerosis). This happens when fatty or calcium deposits cause artery walls to thicken. This can lead to a buildup of fatty material (plaque) in the artery walls. This plaque can suddenly burst (rupture), followed by a blood clot.

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

Who is at risk for thrombosis?

Many of the risk factors for venous and arterial thrombosis are the same.

Risk factors for venous thrombosis may include:

  • A family history of a blood clot in a vein deep in the body (deep vein thrombosis or DVT)

  • A history of DVT

  • Hormone therapy or birth control pills

  • Pregnancy

  • Injury to a vein, such as from surgery, a broken bone, or other trauma

  • Lack of movement, such as after surgery or on a long trip

  • Inherited blood clotting disorders

  • A central venous catheter

  • Older age

  • Smoking

  • Being overweight or obese

  • Some health conditions, such as cancer, heart disease, lung disease, or Crohn's disease

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 

  • Lack of movement, such as after surgery or on a long trip

  • Older age

What are the symptoms of thrombosis?

Symptoms may vary a bit for each person. Symptoms may include:

  • Pain in one leg, usually the calf or inner thigh

  • Swelling in the leg or arm

  • Chest pain

  • Numbness or weakness on one side of the body

  • Sudden change in your mental state

  • Cold arm or leg

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

How is thrombosis diagnosed?

Your healthcare provider will ask about your health history and give you a physical exam. Other tests may include:

  • Ultrasound. This test uses sound waves to check the blood flow in your arteries and veins.

  • Blood tests. These may include tests to see how well your blood can clot.

  • Venography. For this test, a dye is injected into your veins. Then X-rays are taken to show blood flow and look for clots. The dye makes your veins easier to see on the X-rays.

  • MRI, MRA or CT scan. The imaging procedure that is used will depend on the type of blood clot you have and where it is located.

  • Angiography. This imaging test uses a contrast dye to look at the blood vessels.

How is thrombosis treated?

Treatment may include:

  • Blood-thinning medicines (anticoagulants)

  • Thin tubes (catheters)