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Blood clots

A blood clot is a clump of blood that forms in a blood vessel. It is also called a thrombosis.

Blood clots can be very serious and need to be treated quickly. Staying healthy and active can help prevent them.

Types of blood clots

There are two main types of blood clot:

Deep venous thrombosis (DVT)

A DVT is a blood clot that forms in a deep vein, usually in your leg.

Symptoms include:

  • swelling or pain in one leg or calf
  • warmth or redness in a leg

You may not show any symptoms.

Pulmonary embolism (PE)

A PE is when a DVT or part of the DVT travels in the blood and becomes lodged in a blood vessel in your lungs.

Symptoms include:

  • shortness of breath or rapid breathing
  • chest pain, which may be worse when you breathe in
  • a cough or coughing up blood
  • feeling dizzy

Urgent advice: Seek medical help immediately if:

  • you or someone else develops 1 or more symptoms of a blood clot

Emergency action required: Call 112 or 999 or go to your nearest emergency department (ED) if:

  • you or someone else is struggling to breathe
  • someone has passed out

What a blood clot in a leg can look like

The calf of the left leg is red and swollen. The calf of the right leg is pink and is not swollen
A blood clot is causing swelling and redness in the left leg.
The calf of the right leg is red and swollen. The calf of the left leg is white and is not swollen
A blood clot is causing swelling and redness in the right leg.

Check if you're at risk of blood clots

You're more likely to get a blood clot if you:

  • are staying in or recently left hospital
  • are pregnant or had a baby less than 6 weeks ago
  • have active cancer or you're getting cancer treatment
  • cannot move 1 or both legs, for example if your leg is in a cast
  • are overweight

Other things that increase your risk of clots include:

Preventing blood clots

If you're in hospital or at a high risk of blood clots, follow the advice of your care team about preventing clots.

This may mean you:

  • wear compression stockings to improve your blood flow
  • take medicine to reduce your risk (anticoagulants)

There are other things you can do to help avoid clots.


  • keep moving - even if you’re sick in bed, try to move your legs and feet every 90 minutes

  • drink plenty of water to avoid dehydration - your pee should be light yellow or clear


  • do not sit for long periods without moving, if you can avoid it

  • do not drink lots of alcohol as this can make you dehydrated

  • do not smoke

More information is available from Thrombosis Ireland

Page last reviewed: 21 June 2023
Next review due: 21 June 2026

This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.