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Blood clots

5-minute read

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.

Thousands of Australians develop a blood clot in their veins. Most blood clots won’t harm you, but there is a risk they will move through your body and affect your heart, lungs or brain. This can be life threatening, so it’s important to know how to recognise a blood clot.

What are blood clots?

Blood clots are when parts of your blood thicken, forming a semi-solid mass inside a vein. This can happen when:

  • the blood starts to clot more easily (for example, when you’re ill)
  • there are changes to the wall of the vein (for example, if you sit still for a long time)
  • there are changes in how the blood flows

Blood clots can form in veins anywhere in the body, including in the small veins under your skin or in the veins deep inside your body. The medical name for a blood clot is a ‘venous thromboembolism’.

Your blood naturally clots so you don’t lose too much blood if you are injured. Blood clotting becomes a problem when it blocks your blood from flowing properly.

Blood clots can be fatal if they aren’t treated. They can lead to a stroke, heart attack or pulmonary embolism. If you think you may have a blood clot, see your doctor as soon as possible.

Who is at risk of blood clots?

Usually a combination of things leads to a blood clot. You are more likely to develop a blood clot if:

  • you don’t move around for a long period of time (for example, if you are on a long-haul flight)
  • you aren’t moving because you have had surgery
  • you aren’t moving due to an injury, especially a leg injury
  • you have had a blood clot before
  • you have a blood disorder or other condition that makes clotting more likely

Other factors that increase the risk of a blood clot include:

What are the types of blood clot and their symptoms?

Deep vein thrombosis (DVT): A DVT develops when a blood clot forms in one of the veins deep inside your body. They mostly occur in the legs, but you can get a DVT anywhere in your body. The most common symptom is pain and swelling in the affected area, usually your calf or thigh. Sometimes there are no symptoms.

Blood clot in the brain: A blood clot in the brain is called a stroke. The symptoms of a stroke include weakness or drooping in the face, arm or leg, difficulty speaking or understanding, dizziness, blurred vision, severe headache and difficulty swallowing. If you or someone else experiences the signs of stroke, no matter how long they last, call triple zero (000) immediately and ask for an ambulance.

Blood clot in the heart: A blood clot in the heart leads to a heart attack. The symptoms of a heart attack can include chest pain (as though your chest is being pressed or squeezed by a heavy object), shortness of breath, feeling weak and light-headed, nausea, a cold sweat, and feeling anxious. If you have any of these symptoms, or if they get worse quickly or last longer than 10 minutes, call triple zero (000) and ask for an ambulance.

Blood clot in the lungs: If the blood clot travels to your lungs, it’s called a pulmonary embolism. Symptoms include shortness of breath, chest pain, coughing up blood, sweating, rapid heartbeat, feeling dizzy and clammy skin. A major pulmonary embolism can be fatal. If you think you may have a pulmonary embolism, go to the nearest emergency department or call triple zero (000) and ask for an ambulance.

Blood clot in the leg or arm: The most common signs of a blood clot are swelling, tenderness, redness and a warm feeling around the area of the clot. It’s more likely to be a clot if you have these symptoms in just one arm or leg.

Blood clot in the stomach: Symptoms include severe pain and swelling.

How are blood clots diagnosed?

If you think you may have a blood clot, it’s important to see a doctor right away. They will talk to you about what has happened recently and will likely order an ultrasound or a CT scan to view the clot.

You may also have a blood test to look for signs that your blood is clotting more than it should.

How are blood clots treated?

Treatment of a blood clot will depend on where the clot is located. The most common treatment for blood clots is to make your blood thinner using medicines. These medicines include warfarin to stop the blood clot from growing larger and to prevent new clots from forming. You will need to take the medicine for several months and see your doctor regularly to check that it’s working.

Sometimes blood clots are treated with a medicine or procedure to dissolve the clot or to prevent part of it from breaking up and travelling to the lungs, heart or brain.

If you have a DVT, you may be advised to wear compression stockings to help with symptoms and improve the blood flow in your legs.

If you have a heart attack, stroke or pulmonary embolism, you will need to have emergency treatment in hospital.

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Last reviewed: April 2021

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