What is VTE and why do hospitals assess for it?
Venous thromboembolism (VTE) covers two linked problems. A deep vein thrombosis (DVT) is a clot in a deep vein, usually in the leg or pelvis. A pulmonary embolism (PE) happens when a clot travels to the lungs. PE can kill, and DVT can leave people with long-term leg pain, swelling and ulcers.
Admission to hospital raises the risk a great deal. Patients lie still, become dehydrated, have operations and are acutely unwell. A clot that develops in hospital, or within about 90 days of an admission, is usually called hospital-acquired thrombosis. Many of these clots can be prevented, which is why VTE prevention has been a patient safety priority in England for many years and why trusts audit their assessment rates and review cases where a clot developed.
The three classic contributors are described by Virchow's triad. Knowing them helps you think about risk rather than just ticking boxes.
| Factor | What it means | Hospital examples |
|---|---|---|
| Stasis | Blood flow slows | Bed rest, long operations, paralysis, dehydration |
| Hypercoagulability | Blood clots more readily | Cancer, pregnancy, oestrogen-containing medicines, infection and inflammation, thrombophilia |
| Vessel wall damage | Injury to the vein lining | Surgery (especially orthopaedic), trauma, central venous catheters |
When should a VTE risk assessment be done?
NICE NG89 covers people aged 16 and over. It recommends assessing medical, surgical and trauma patients for both VTE risk and bleeding risk as soon as possible after admission, or by the time of the first consultant review. Acute psychiatric inpatients should be assessed in the same way, a group that is easy to forget.
One assessment on admission is not enough. Reassess:
- at the consultant review
- whenever the clinical condition changes, such as after surgery, a new diagnosis, bleeding or a change in mobility
- when a new risk factor appears, for example a new medicine that raises bleeding risk
- before discharge, to decide whether prophylaxis should continue at home
Pregnant women and women who have recently given birth, miscarried or had a termination have their own assessment points. These follow tools from a national body such as the Royal College of Obstetricians and Gynaecologists (RCOG), and are set out in NG89 and RCOG Green-top Guideline 37a.
What counts as a VTE risk factor and a bleeding risk factor?
The Department of Health tool starts with mobility and the type of admission, then asks about patient-related factors. The lists below are examples to help understanding, not a substitute for your trust's tool.
| VTE risk factors (examples) | Bleeding risk factors (examples) |
|---|---|
| Significantly reduced mobility | Active bleeding |
| Hip or knee replacement, hip fracture | Acquired bleeding disorders such as acute liver failure |
| Surgery with a long anaesthetic time | Already taking anticoagulants |
| Active cancer or cancer treatment | Low platelet count |
| Age over 60, obesity, dehydration | Uncontrolled high blood pressure |
| Personal or first-degree family history of VTE | Acute stroke |
| Oestrogen-containing contraception or HRT | Untreated inherited bleeding disorders such as haemophilia |
| Pregnancy or the postnatal period | Planned procedures with high bleeding risk, such as lumbar puncture or neurosurgery |
The key judgement is the balance. Prophylaxis is offered when the risk of VTE outweighs the risk of bleeding. Someone with several clot risk factors and no bleeding concerns is a clear case. Someone with a recent bleed and limited mobility needs a different plan, often mechanical rather than drug prophylaxis.
Which prophylaxis: LMWH, stockings or IPC?
Pharmacological prophylaxis
Low molecular weight heparin (LMWH), such as enoxaparin or dalteparin, is the usual first choice in UK hospitals. NG89 also includes fondaparinux, unfractionated heparin (for example in severe kidney impairment) and, for some orthopaedic patients, direct oral anticoagulants or aspirin. For acutely ill medical patients whose clot risk outweighs bleeding risk, NG89 recommends starting as soon as possible, within 14 hours of admission, and continuing for at least 7 days.
Doses are not one size fits all. Prophylactic LMWH may need adjusting for kidney function and for very low or high body weight. Check the BNF, your local formulary and a pharmacist. Give doses at a consistent time each day, and plan timing carefully around surgery and spinal or epidural procedures.
Mechanical prophylaxis
Anti-embolism stockings and intermittent pneumatic compression (IPC) are used when drug prophylaxis is contraindicated, or alongside it in some surgical groups. Stockings can cause harm if fitted to the wrong person.
If stockings are used, measure the legs, use the right size, and remove them daily to wash and inspect the skin, especially over the heels and bony areas. Whatever else is prescribed, encourage early mobilisation and good hydration unless there is a clinical reason not to.
How does it work for different patient groups?
NG89 has detailed recommendations by group. The summary below is for orientation. Durations, agents and aspirin doses for orthopaedic patients in particular must be checked in the full guideline and your local protocol.
| Group | Key points to check |
|---|---|
| Acutely ill medical patients | Drug prophylaxis if clot risk outweighs bleeding risk; start within 14 hours of admission; minimum 7 days |
| Elective hip or knee replacement | Several options (LMWH, aspirin, a DOAC, sometimes with stockings) with set durations; follow local orthopaedic protocol |
| Fragility fracture of hip, pelvis or proximal femur | Drug prophylaxis for about one month if clot risk outweighs bleeding risk |
| Major abdominal or pelvic cancer surgery | Consider extended prophylaxis to 28 days after surgery |
| Acute stroke | No stockings; consider IPC for immobile patients; specialist team decides on drug prophylaxis |
| Acute psychiatric inpatients | Assess on admission; consider LMWH if clot risk outweighs bleeding risk |
| Pregnancy and up to 6 weeks after birth | Use an RCOG-based tool at booking, on admission and after birth |
Patients already on full-dose anticoagulation, for example for atrial fibrillation, usually do not need extra prophylaxis. The risk is that their usual anticoagulant gets omitted during the admission. If it is stopped, say before surgery, think again about prophylaxis. Patients on antiplatelet medicines need an individual look at combined bleeding risk.
Worked example: getting the assessment right
Margaret is usually independent but is now bed-bound with pneumonia. She had a DVT ten years ago. Her platelets are normal, her blood pressure is controlled, she takes no anticoagulant, and her creatinine clearance is reduced. The admitting doctor completes the trust tool: high VTE risk (acutely ill, immobile, over 60, previous DVT, infection) and no significant bleeding risk. LMWH is prescribed to start within 14 hours. The ward pharmacist spots the reduced kidney function and recommends an adjusted dose, which the doctor amends. Margaret is told why she is having injections and which symptoms to report, and given a leaflet. The plan is confirmed at the next morning's consultant review.
Compare two ways of documenting that decision.
VTE assessment done. Enoxaparin 40 mg OD.
VTE risk assessment completed with trust tool. VTE risk: acutely ill medical, bed-bound, age 76, previous DVT, pneumonia. Bleeding risk: none identified (platelets normal, not anticoagulated, BP controlled). Plan: LMWH within 14 hours of admission, dose adjusted for reduced creatinine clearance after pharmacist review. Patient informed, agrees, leaflet given. Encourage mobility and fluids. Reassess at consultant review or if condition changes.
The weak entry gives a dose that may be wrong for her kidneys and shows no reasoning. The strong entry shows both sides of the balance, the safety check, the conversation and when to look again. If a clot develops later, a review can see that the decision was sound.
Common VTE safety problems and how to avoid them
- Assessment missed or never repeated: Complete on admission, review at consultant review and whenever the condition changes. Use electronic prompts and check them on ward rounds.
- Omitted doses: Record the reason for any missed dose and escalate omissions. Doses held for a procedure must be restarted, so check the plan afterwards.
- Wrong dose: Check weight and kidney function before prescribing LMWH and involve a pharmacist.
- Stockings on the wrong legs: Check for arterial disease, neuropathy, skin problems and stroke before fitting, and inspect the skin every day.
- Epidural and spinal timing: Follow local guidance on LMWH timing around neuraxial anaesthesia and catheter removal. If unsure, ask the anaesthetist rather than giving or omitting by guesswork.
- Heparin-induced thrombocytopenia: Watch for an unexpected fall in platelets or a new clot in a patient on heparin, follow local monitoring policy and seek haematology advice.
What to tell patients and what to do at discharge
NG89 recommends giving people spoken and written information before prophylaxis starts: their risk, why prophylaxis matters, possible side effects, and what they can do themselves, such as staying mobile and drinking enough. People should be involved in the decision, and some will decline injections, which needs a documented discussion of alternatives.
- Reassess whether prophylaxis should continue after discharge.
- If it continues, check the patient or a carer can give the injections or take the tablets, and knows for how long and who to contact with problems.
- Explain how to wear and care for stockings if prescribed, and when to stop.
- Explain symptoms to act on urgently: a painful, swollen or red leg, sudden breathlessness, chest pain or coughing up blood.
- Put the plan in the discharge summary for the GP.
Learning more
This guide is educational. Always follow NICE NG89, your trust's VTE policy and approved tool, and pharmacist advice for individual patients. If you want to work through the assessment, prophylaxis choices and worked medical and surgical cases in more depth, with a reflective exercise for your CPD record, the Venous Thromboembolism Prevention course covers this material. Because VTE can present as a sudden collapse, keeping your resuscitation skills current through accredited hands-on training also matters.
Frequently asked questions
How soon after admission should a VTE risk assessment be done?
NICE NG89 recommends assessing VTE and bleeding risk as soon as possible after admission, or by the time of the first consultant review. It should then be repeated at consultant review, whenever the patient's condition changes, and before discharge. Many trusts build this into the electronic record so it prompts the admitting clinician, but responsibility for completing it still sits with the team.
Who is responsible for completing the VTE risk assessment?
Usually the admitting doctor or a non-medical prescriber completes the assessment and prescribes prophylaxis. Nurses check it has been done, give prophylaxis, fit and monitor stockings and encourage mobility. Pharmacists check doses, kidney function, interactions and omissions. Local policy sets out exact responsibilities, but anyone who notices a missing assessment should raise it.
What tool is used for VTE risk assessment in the UK?
NG89 asks for a tool published by a national UK body, professional network or peer-reviewed journal. The Department of Health VTE risk assessment tool is the most widely used for medical and surgical adults. In pregnancy and after birth, a tool based on RCOG guidance is used. Always use the version approved by your organisation.
How long should VTE prophylaxis continue for medical patients?
For acutely ill medical patients whose clot risk outweighs bleeding risk, NG89 recommends drug prophylaxis for a minimum of 7 days. Some surgical and orthopaedic groups need longer courses, including up to 28 days after major abdominal cancer surgery. Check the full guideline and your local protocol, and reassess whenever the patient's condition changes.
Who should not wear anti-embolism stockings?
Do not use them in people with suspected or proven peripheral arterial disease or arterial bypass grafts, peripheral neuropathy or sensory impairment, fragile skin, dermatitis or recent skin grafts, severe leg oedema, material allergy, or legs that cannot be fitted correctly. NG89 also advises against them for VTE prevention in acute stroke, where intermittent pneumatic compression can be considered.
Does a patient on a DOAC or warfarin need VTE prophylaxis as well?
Usually not, if they are taking full-dose anticoagulation and it continues during the admission. The common error is omitting their usual anticoagulant without a plan. If it is stopped, for example before surgery, prophylaxis may be needed. Each case should be reviewed with the prescriber and pharmacist and the decision recorded.
Why does LMWH dose depend on kidney function and weight?
LMWH is cleared largely by the kidneys, so it can build up when kidney function is poor and increase bleeding risk. Standard prophylactic doses may also be too much or too little at extremes of body weight. Check creatinine clearance and weight, use the BNF and local formulary, and ask a pharmacist when in doubt.
Related courses
Venous Thromboembolism Prevention
This course explains how to prevent hospital-acquired venous thromboembolism in adults, following NICE guideline NG89. It covers risk assessment,…
Adult Advanced Life Support (UK Guidelines)
This course explains the recognition and management of adult in-hospital cardiac arrest, based on the current Resuscitation Council UK adult advanced…
Paediatric Life Support (UK Guidelines)
This course teaches the recognition of the seriously ill or injured child and the management of paediatric cardiorespiratory arrest, based on current…
Sources and further reading
- Venous thromboembolism in over 16s: reducing the risk of hospital-acquired deep vein thrombosis or pulmonary embolism (NG89). National Institute for Health and Care Excellence.
- Venous thromboembolism in adults: reducing the risk in hospital (QS3). National Institute for Health and Care Excellence.
- Risk assessment for venous thromboembolism (VTE). Department of Health.
- Reducing the risk of venous thromboembolism during pregnancy and the puerperium (Green-top Guideline 37a). Royal College of Obstetricians and Gynaecologists.
- British National Formulary: low molecular weight heparins. BMJ Group and Royal Pharmaceutical Society.
Practitioner Insight is an independent education provider. It is not affiliated with or endorsed by the GMC, MPTS, NMC, HCPC, GPhC or any NHS organisation, and this information is not legal advice. If you have been referred to a regulator, speak to your defence organisation, trade union or legal representative.
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