Blood clots and lowering your risk

This risk of getting a blood clot is higher when you are in hospital and up to 90 days after leaving hospital. These are known as hospital-associated blood clots.

Deep vein thrombosis (DVT) is a blood clot in a deep blood vessel. It usually happens in your leg or pelvis (the area between the hip bones, in the lower part of the tummy). DVT might cause pain or swelling. You might have no symptoms.

A blood clot is not life-threatening by itself. However, sometimes it can move out of position and travel, blocking the blood supply to your lungs. This type of blood clot is called a pulmonary embolism (PE) and can be life threatening. You need treatment straight away if you have any symptoms including:

  • chest pain
  • breathlessness
  • feeling sweaty and unwell
  • collapsing
  • occasionally coughing up blood

We use the term venous thromboembolism (VTE) for both DVT and PE.

The NHS website has more information about DVT and PE.

When to get help after leaving hospital

If you have left the emergency department (A&E) or urgent care centre with a lower limb plaster cast, splint or walker boot, it's important to know about blood clots and deep vein thrombosis (DVT).

Ask for an urgent GP appointment or call 111 if:

  • you have new unexplained pain in your leg
  • you have new swelling in your leg
  • you have warm or discoloured skin on your leg

Call 999 or go to A&E if:

  • you are breathless
  • you have pain in your chest, back or ribs that might be worse when you breathe in
  • you collapse
  • you are coughing up blood

These can be signs that the blood clot has travelled to your lungs and caused a pulmonary embolism.

Who is at risk of blood clots

When you are admitted to hospital, a healthcare professional will assess you for your risk of getting a blood clot. If you are at risk, we will talk to you about what we offer to protect against clots.

Most unwell adults admitted to hospital are at risk. You are at increased risk of getting DVT if your mobility (movement) is reduced for a while.

Some people are more likely to get DVT than others. DVT is more likely to happen if you:

  • are over 60
  • are overweight or obese
  • are dehydrated
  • take the oral contraceptive pill (but not patch) or hormone replacement therapy (HRT)
  • have cancer or cancer treatment
  • have a condition that makes your blood ‘sticky’ (more likely to clot)
  • have inflamed varicose veins (phlebitis)
  • previously had blood clots or have a family history of blood clots
  • are pregnant or have recently given birth
  • have a long-term medical condition, such as heart or lung disease, or diabetes
  • have had surgery
  • have had a significant injury or physical trauma

How to lower your risk of blood clots

Your doctor or nurse assesses your individual risk of getting DVT.

To reduce your risk, try to:

  • take blood-thinning medicines if we prescribe them
  • wear calf or foot pumps (inflatable sleeves) if you are given these. These inflate automatically to increase blood flow in your legs
  • stay active and exercise if you can. If you cannot walk, move your legs, ankles and feet around as much as possible. When in hospital, you can ask your nurse or physiotherapist for more information
  • drink plenty of fluids to avoid becoming dehydrated (unless you are told otherwise)

Blood-thinning medicine

Your doctor might prescribe a medicine that thins your blood and stops it from clotting as quickly as normal. This is called an anticoagulant. Usually it is given as an injection and sometimes as a tablet.

If you need to take these medicines when you leave hospital, you will be told how long to take them for. The anticoagulant most often used is a type of heparin, which is given by injection. Blood-thinning tablets may be given to you after hip and knee replacement.

If you need an injection of anticoagulation medicine, the doctor or nurse will explain how to do this safely. If you have an injection, you may get some discomfort and bruising around the injection site. This should improve when the injections stop. It is rare to have problems with bleeding after the injection.

To be effective, these medicines must be used correctly. If you have any questions or concerns, please ask your doctor or nurse.

If you have any unusual bleeding, contact a GP. In an emergency, go to your nearest emergency department (A&E).

Calf or foot pumps

We might ask you to wear calf or foot pumps (also called special inflatable sleeves) around your legs or feet while you are in bed or sitting still in a chair. These will inflate automatically at regular intervals, providing pressure to increase blood flow out of your legs.

Keeping healthy

Try to keep a healthy weight and do regular exercise. You can find more information in our vital 5 ways to stay healthy.

Contraceptive medicine or HRT

Before going to hospital, tell your doctor if you are taking contraceptive medicine or hormone replacement therapy (HRT).

Your doctor may consider stopping them in the weeks before an operation and give advice on the temporary use of other methods if your usual contraceptive is stopped.

Investigating hospital-associated blood clots

If you develop a blood clot as a result of a recent hospital admission and within 90 days of discharge from your discharge, we will carry out an investigation to help identify why this happened.

It may be several weeks before the outcome is known and you may ask for the result at your next consultation.

Useful sources of information

Thrombosis UK is a charity promoting awareness, research and care of thrombosis. They have more information on preventing hospital associated blood clots. Call 0300 772 9603

Let's Talk Clots is a free app developed by Oxford University Hospitals NHS Foundation Trust and Thrombosis UK. The app provides medically-approved information about reducing the risk of blood clots, signs and symptoms, and recovering after a blood clot.

Ref number: 4288/VER4
Last reviewed: February 2024
Next review: February 2027

Trusted Information Creator. Patient Information Forum

Contact us

If you have any questions or concerns, please call the emergency department at St Thomas’ Hospital.

Phone: 020 7188 2127 (24 hours)

If you develop a blood clot in hospital, or after you've been discharged, please let the thrombosis team know.

Phone: 020 7188 2781

Do you have any comments or concerns about your care?

Contact our Patient Advice and Liaison Service (PALS)

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