Where do blood clots develop?

Blood clots form in the deep veins of the leg or in the lungs. A blood clot in the leg is called a deep vein thrombosis (DVT). If the clot dislodges and travels to the lung, then this is called a pulmonary embolism (PE).

How do blood clots develop?

Blood clots form when blood flow in the veins of the legs is slow or when the blood-clotting proteins increase and make the blood thicker. Your blood flow can slow down when you are lying in bed for long periods of time and do not use your muscles. Your blood-clotting proteins usually increase with inflammation or after surgery.

What are the symptoms?

A blot clot in the leg can cause pain and swelling in that leg. A blood clot in the lung is more serious and can lead to breathlessness, coughing, blood-stained spit, chest pain and occasionally you may collapse. In rare cases, a blood clot can be fatal.

What happens if I have a blood clot?

A blood clot in the vein should be diagnosed and treated without delay. If you develop any of the above symptoms or signs during your hospital stay, please inform the nurse or doctor looking after you immediately. After discharge, you should go to your GP or your local emergency department for an assessment. You will have a scan to confirm the blood clot and receive treatment.

Could it happen to me?

Anybody who is bed-bound in hospital is at an increased risk of developing a blood clot. Other factors that increase the risk of developing a blood clot include:

  • If you are older than 60 years of age
  • If you are overweight
  • If you have cancer
  • If you have heart or lung problems that require treatment
  • If you have been admitted for severe infection or inflammation
  • If you have a personal or family history of blood clots in the legs or lungs
  • If you have a blood condition that increases the risk of blood clots (thrombophilia)
  • If you are taking hormone replacement therapy (HRT) or an oestrogen-containing contraceptive pill
  • If you have severe varicose veins with phlebitis
  • If you are pregnant
  • If you have been admitted for an operation on the pelvis and/or legs lasting more than 60 minutes
  • If you have been admitted for any operation which is likely to last more than 90 minutes

What can I do?

You can play an active part in reducing your risk of developing a blood clot in a vein. During your hospital stay, you should try to move around as much as possible. Moving your legs, even when you are lying in bed, will improve blood flow and reduce the risk of blood clots. Dehydration can also increase the risk of blood clots, so it is important to ensure good fluid intake to help prevent this.


  • Your doctor or nurse will inform you when it is safe for you to get out of bed after surgery.
  • While you are in bed, leg exercises are very important. Please ask your nurse to show you what to do.

Fluid intake

  • Avoid getting dehydrated and drink enough fluids (one to two litres a day).

What else can be done?

When you are admitted to hospital, your medical team will assess your risk of developing a blood clot. They will then decide what preventative steps are appropriate for you. The options include:

Compression stockings

Compression stockings can improve blood flow in the veins in the legs. You will be assessed to decide whether you should use them, as they are not suitable for all patients. The compression stockings will be measured and fitted, and you will be shown how to put them on.

To be effective, they should be pulled up to avoid creases. They should be removed every day, and your skin should be checked for any blisters or red/bruised areas. You will need to wear your compression stockings until you are back to your usual mobility.


Flowtrons are inflatable cuffs that are wrapped around the calves and squeezes them. The cuffs are connected to a machine. This improves the blood flow in the veins of the legs.

Heparin injections

Heparin is medication that can be used to make the blood thinner. It is usually given once a day as an injection under the skin. Possible side effects include bruising at the injection site and prolonged bleeding if you cut yourself (this is rare). Heparin is of animal origin. Please talk to your doctor if this is of concern to you.

After discharge

There is still a possibility that you could develop a blood clot in the days and weeks following your discharge until you are back to your normal activity level.

Once you are home, you should avoid long periods of bed rest during the day. You should try to stay active, wear your compression stockings and drink plenty of water. Please contact your GP urgently if you are not able to mobilise at home for any reason.

Some patients with a higher risk of developing blood clots will be discharged with heparin injections. This will be explained to you before you go home, and you will be taught how to give the injections yourself. You will be given a 'sharps bin' to safely dispose of the syringes. The bin should be taken to your GP or local pharmacy once you have completed the course.

Orthopaedic patients who have had a procedure may be discharged with tablets to prevent blood clots. If you develop symptoms of a blood clot in the leg or lungs after discharge, you should seek urgent medical advice or visit your nearest accident and emergency department.

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