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The AstraZeneca COVID-19 vaccine has been linked to a very rare blood-clotting disorder called 'thrombosis with thrombocytopenia syndrome’ (TTS). You can read about it here. If you're experiencing any symptoms following a COVID-19 vaccination, you can use the COVID-19 Vaccine Side Effect Checker.

What is thrombosis?

Thrombosis occurs when a blood clot forms either in a vein or an artery. The clot is known as a thrombus.

Normally, blood clots only form when you cut yourself and start to bleed. At the site of the cut, the blood gets thicker and forms a clot to ‘plug up’ the wound so it stops bleeding.

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.

When should I call an ambulance/go to the ED?

A thrombosis can be life threatening. Call an ambulance or go to the emergency department if:

  • you have chest pain
  • you cough up blood
  • you are short of breath
  • your mouth has drooped
  • you can’t lift both arms
  • your speech is slurred
  • you feel faint or pass out
  • you are nauseous or vomiting
  • you are numb and weak down one side
  • you are confused and having difficulty understanding
  • one of your legs is a different colour to the other one

CHECK YOUR SYMPTOMS — Use the Symptom Checker and find out if you need to seek medical help.

What should I do while waiting for the ambulance?

You or the person you are looking after should stop what they are doing and sit or lie down in a comfortable position. Loosen any tight clothing. Do not eat or drink anything.

If their condition worsens and they stop breathing, start CPR.

What are the warning signs/symptoms of thrombosis?

A superficial thrombus can cause pain, swelling and redness over and around the site of the clot.

A DVT in the leg or pelvis can cause pain and swelling.

What causes 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 overweight or obese
  • are pregnant
  • have cancer
  • are undergoing hormone therapy (including taking oral contraceptives)
  • have a blood disorder
  • are dehydrated
  • have had a DVT before

ARE YOU AT RISK? — Are you at risk of type 2 diabetes, heart disease or kidney disease? Use the Risk Checker to find out.

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

How is thrombosis diagnosed?

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.

FIND A HEALTH SERVICE — The Service Finder can help you find doctors, pharmacies, hospitals and other health services.

How is thrombosis treated?

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.

ASK YOUR DOCTOR — Preparing for an appointment? Use the Question Builder for general tips on what to ask your GP or specialist.

Can thrombosis be prevented?

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.

Complications of thrombosis

People with a superficial thrombus sometimes also have a deep vein thrombosis.

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.

If you have a DVT, bits of the clot can break off and travel to the lungs, causing pulmonary embolism. This is life threatening.

More information

Find out more about warfarin and other anticoagulants here.

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: April 2020

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