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Information for patients, relatives and carers

What are hospital-associated blood clots?

A hospital-associated blood clot happens in patients either when you are in hospital or up to 90 days after you are discharged. There are two kinds:

1. Deep-vein thrombosis (DVT): a DVT is a blood clot that forms in a deep vein, most commonly in your leg or pelvis. lt may cause no symptoms at all or cause pain, swelling or discoloration of the leg (red, purple or blue changes).

2. Pulmonary embolism (PE): if all or part of the clot breaks free and passes through your blood vessels, it can reach your lungs. This is called a PE. Symptoms include: chest pain, breathlessness or collapse or coughing (with blood- stained phlegm).

If you develop any of these symptoms, either in hospital or after you go home, please get medical advice immediately.
Health professionals use the term venous thromboembolism (VTE), to cover both DVT and PE.

Are blood clots common?

Blood clots happen in the general population in about one in 1000 people every year. You may have heard about people getting a DVT after flying, but you are much more likely to get a blood clot after going into hospital. In fact, about two-thirds of all blood clots happen during or in the 90 days after a stay in hospital.
Although these risks are still small, the consequences can be serious. Blood clots can lead to long-term medical problems such as permanent swelling in the leg, varicose veins, and even leg ulcers. They can even lead to death.

The Government knows that hospital-associated blood clots are an important problem and have asked hospital doctors, nurses and pharmacists to assess your risk. If you are at risk, your doctor or nurse will talk with you about what will be done to protect you against clots. Remember, it’s ok to ask if you are unsure about your own risk.

Who is at risk?

Any adult who is unwell and admitted to hospital is at risk. Other factors that put people at greater risk include the following:

  • A previous clot
  • A diagnosis of cancer
  • Immobility compared to pre hospital admission
  • Taking oestrogen-containing contraceptives and hormone replacement
  • Having an operation
  • Suffering a significant injury or trauma
  • Being pregnant and after giving birth
  • Dehydration
  • Smoking
  • Being overweight (body mass index (BMI) of more than 30)
  • Varicose veins
  • Certain 'sticky blood' conditions such as antiphospholipid syndrome or Factor V Leiden
  • Being older than 60

What can I do to reduce my risk?


If you are admitted to hospital, you might be measured and fitted with anti-embolism stockings for your legs. You should be shown how to wear them and told to tell a health professional about any new pain or discomfort in your feet or legs. Your stockings will be removed for a short time once a day so that you can have a wash and check for any skin problems. If you have any question or concerns it is ok to ask the nurse/doc

Inflatable sleeves

The clinical team may ask you to wear calf or foot pumps. These are special inflatable sleeves which you wear around your legs or feet while you are in bed or sitting still in a chair. These will inflate automatically and provide pressure at regular intervals, increasing blood flow out of your legs.

Blood thinners

Most patients at risk will be prescribed a small dose of an anticoagulant. This reduces the chance of having a blood clot by thinning your blood slightly. If you need to take a blood thinner when you leave hospital, you will be told how long to take it for. The blood thinner most often used is a type of heparin, which is given by injection. Heparin comes from animals. If you have any concerns about using animal products, please tell your doctor and they will discuss other options with you. Blood-thinning tablets are increasingly being used after Orthopaedic surgery.
To be effective, you must use these methods of prevention correctly. It is ok to ask your doctor or nurse if you have any questions or concerns.

What can you do to help yourself?

If possible, before you come into hospital:

•Talk to your doctor about contraceptives or hormone- replacement therapy (your doctor may consider stopping these in the weeks before an operation and will provide advice on temporarily using other methods if you stop taking your usual contraceptive);
•Stop smoking
•Keep a healthy weight; and
•Do regular exercise

When in hospital:

•Keep moving or walking and get out of bed as soon as you can after your operation-ask your nurse or physiotherapist for more information;
•If you are not able to get out of bed, do gentle leg exercises such as leg lifts and ankle circles (the more you do this, the better);
•Take deep breaths hourly to improve circulation;
•Ask your doctor or nurse: "What is being done to reduce my risk of clots?” and
•Drink plenty of fluid to keep hydrated.

What happens when I go home?

There are several things you can do when you are discharged to help prevent blood clots occurring, such as getting regular exercise (e.g., walking regularly); drinking plenty of water; maintaining a healthy weight or losing weight if you are obese; and stopping smoking.

Until you return to your usual level of activity, you may need to wear anti-embolism stockings after you go home. Your nurse will tell you how to put them on and what you should check your skin for.

If you need to continue anticoagulation injections at home, your nursing team will teach you how to do this. If you have any concerns, make sure you speak to a nurse before you leave. It’s ok to ask if you are unsure as to why you are having to continue anticoagulation at home.

If you develop any signs or symptoms of a clot when you are at home, such as: chest pain, shortness of breath or collapse, immediately contact your GP or your nearest hospital’s emergency department.

➢ Please ask your doctor or nurse for more information.

Useful sources of information

•NHS 111– You can call 111 when you need medical help fast but it’s not a 999 emergency. The NHS 111 service is staffed by a team of fully trained advisers, supported by experienced nurses and paramedics. NHS 111 is available 24 hours a day, 365 days a year. Please visit
•NHS website patient information on blood clots. Please visit
•Thrombosis UK also has more information. Please visit
Patient Advice and Liaison Service (PALS) – To make comments or raise concerns about the Trust’s services, please contact PALS.

Your questions

Always ask anything you wish, no questions are trivial or ‘silly’. The person you ask will do their best to answer but, if they don’t know, they will find someone else who is able to discuss your concerns. 

To access this information in another format or language


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Please contact the patient advice and liaison service (PALS)

Frimley Park Hospital 0300 613 6530

Heatherwood Hospital and Wexham Park Hospital 0300 615 3365

Title of Leaflet Preventing hospital-associated blood clots
Author Dr N Philpott Consultant
Department Clinical Haematology
Ref. No R/010/5
Issue Date June 2023
Review Date June 2026

Legal Notice
Please remember that this leaflet is intended as general information only. We aim to make the information as up to date and accurate as possible. Please therefore always check specific advice or any concerns you may have with your doctor.