Thrombosis occurs when a blood clot forms either in a vein or an artery even though you are not bleeding. The clot is known as a thrombus.

Normally, blood clots only occur when you bleed. The blood gets thicker so that the bleeding stops. If you did not get blood clots, you would bleed to death.

Types of thrombosis

If you have a blood clot in a vein near the skin, it is known as superficial thrombosis. This can be painful, but is usually not serious.

If a clot forms in your artery, this is known as arterial thrombosis. This can cause serious problems.

When a blood clot forms in the veins deep inside your body it is called deep vein thrombosis, or DVT. This too can cause serious problems.

Problems caused by thrombosis

A superficial thrombus can cause pain, swelling and redness over and around the site of the clot. However, people with a superficial thrombus sometimes also have a deep vein thrombosis.

If a DVT forms in the leg or pelvis, it can cause pain and swelling. But more importantly, bits of the clot can break off and travel to the lungs, causing pulmonary embolism.

If you have an arterial thrombus in the heart, it can cause a heart attack. An arterial thrombus in an artery in the head or neck can cause a stroke.

Risk factors for thrombosis

Arterial thrombosis usually affects people whose arteries are clogged with fatty deposits. This causes the arteries to get narrower and harder.

You are more likely to develop thrombosis in your veins if you:

  • have recently had surgery
  • smoke
  • have been immobile for long periods
  • are pregnant
  • have cancer
  • are undergoing hormone therapy (including taking oral contraceptives)
  • have a blood disorder
  • are dehydrated
  • have had a DVT before. 

Travelling by plane also increases your risk of a DVT, but only slightly. Other risk factors are more important. 

Diagnosing thrombosis

Your doctor will talk to you about your overall health and lifestyle, and will examine you. If your doctor suspects you might have thrombosis, they might order one or more tests, such as an ultrasound scan, a blood test or an x-ray

Treatment of thrombosis

If you have had a superficial thrombosis, there are several treatment options, including medication, surgery and bandaging of the affected limb.

The treatment of an arterial or deep vein thrombosis will depend on where it is, and the extent of any damage done. It might require hospitalisation.

Some people are advised to have surgery to remove or bypass a blood clot, or to widen an artery. Others are prescribed medicines to dissolve the clot. Compression stockings can relieve swelling and pain in the legs.

Some people are prescribed an anticoagulation medicine, like warfarin, to thin the blood and make it less likely to clot. Sometimes, anticoagulation medicines need to be taken for months or years to prevent clots recurring.

Prevention of thrombosis

The usual ways to reduce your risk of thrombosis are to:

  • quit if you smoke
  • cut down on alcohol if possible
  • lose weight if you need to
  • exercise more if possible
  • eat healthy food.

Some people are advised to wear compression stockings, especially on long flights and after surgery. 

Some are advised to take a low dose of aspirin each day to thin their blood.

If you are at risk of arterial thrombosis, a doctor might also recommend medicines to reduce your cholesterol and blood pressure.

More information

Find out more about warfarin and other anticoagulants here.


MyVMC (Blood clotting: International normalised ratio) 

ANZSVS (Deep venous thrombosis) 

Healthy WA (Deep vein thrombosis) 

NHS Choices (Arterial thrombosis)

MyVMC (Pulmonary embolism)