What is DVT and why does surgery increase the risk?

A deep vein thrombosis (DVT) is a blood clot that forms in a deep vein, usually in the calf, thigh or pelvis. Surgery increases DVT risk through three mechanisms — known as Virchow's triad: reduced blood flow from immobility, damage to blood vessel walls during surgery, and changes in blood coagulation triggered by the body's response to injury. Source: NICE NG89: Venous thromboembolism in adults (last checked Oct 2026).

The most serious consequence is pulmonary embolism (PE), when a clot breaks off and travels to the lungs. The good news: DVT after surgery is largely preventable with the right measures, and NICE NG89 is the guidance used across the NHS to reduce this risk. Source: NHS: Deep vein thrombosis (last checked Oct 2026).

Risk factors that affect your DVT risk after surgery

DVT risk after surgery is not the same for everyone. NICE NG89 identifies risk factors that, when present, significantly increase the chance of a clot forming — procedure type and personal risk factors together determine overall risk.

Type of surgery: lower limb and pelvic surgery carry the highest risk. Hip replacement and knee replacement have among the highest DVT rates. Day procedures carry much lower risk.
Duration of surgery: procedures lasting more than 90 minutes increase risk. General anaesthetic for more than 60 minutes on the pelvis or lower limb is a specific risk threshold in NICE guidance.
Immobility after surgery: being unable to walk or move freely for more than 3 days significantly increases risk. Early mobilisation is one of the most effective preventive measures.
Previous DVT or PE: a personal history of blood clots substantially increases recurrence risk around surgical stress.
Age: risk increases with age, particularly above 60.
Active cancer or cancer treatment: cancer is associated with a prothrombotic (clot-forming) state.
Obesity (BMI over 30): a known independent risk factor, particularly combined with surgery and immobility.
Dehydration: thickens the blood and is a modifiable risk factor.
Thrombophilia: inherited or acquired clotting disorders significantly increase risk.

Source: NICE NG89: risk factor assessment (last checked Oct 2026)

How DVT is prevented after surgery

VTE (venous thromboembolism) prevention is a core part of post-operative care across the NHS. NICE NG89 sets out the recommended approach.

Anticoagulant injections (low molecular weight heparin, such as enoxaparin or dalteparin) are the primary pharmacological prevention. NICE NG89 gives different durations for hip and knee replacement: around 28–35 days after hip replacement, but about 14 days after knee replacement.
Anti-embolism (TED) stockings: maintain blood flow in the leg veins. They work best combined with other prevention methods and should be correctly fitted by your team.
Mechanical compression devices: inflate around the calves while you're in bed, mimicking walking. Commonly used during and after surgery.
Early mobilisation: getting up and walking as soon as safely possible is one of the most effective strategies. Even moving your feet and ankles in bed helps.
Hydration: adequate fluid intake prevents blood from thickening, unless your surgeon has restricted fluids.

Source: NICE NG89: VTE prevention in adults (2018, reviewed 2024, last checked Oct 2026)

Symptoms to watch for

⚠ Contact your team if you have

Calf pain, tenderness or aching in one leg
Swelling of one calf or lower leg
Warmth or redness in one leg
Visible surface veins becoming more prominent

🚨 Call 999 immediately if

Sudden shortness of breath
Chest pain or pressure
Coughing up blood
Rapid heart rate with any of the above

Do not wait for symptoms to improve on their own; seek assessment promptly — or call NHS 111 for urgent, non-emergency advice.

Source: NHS: DVT symptoms (last checked Oct 2026)

Not in the UK? See our Australian DVT risk checker instead.

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Welcome — a quick note first

This UK guide is compiled from published NHS and NICE guidance. Some pages include Amazon affiliate links — these never influence clinical content.

This is general information, not medical advice. It cannot replace what your own surgical team, GP or NHS 111 tells you.

⚠ In an emergency, call your local emergency number: 000 (Australia) · 111 (New Zealand) · 999 (UK, Ireland & Singapore) · 911 (USA & Canada) · 112 (European Union & India) · or your country's equivalent. On most mobile networks worldwide, 112 also works as a backup even without a SIM card or when the phone is locked. For urgent but non-emergency advice in the UK, call NHS 111.

If anything here contradicts what your treating team has told you, follow them, not us.