Quick answer

What is deep vein thrombosis?

Deep vein thrombosis is a blood clot in a deep leg vein — causing calf or thigh pain, swelling, warmth, and redness, often one leg only. Part of the clot can break off causing pulmonary embolism (PE) — chest pain and breathlessness — a medical emergency. Risk increases after surgery, immobility, pregnancy, and the combined pill. Treated with anticoagulants (DOACs or heparin/warfarin). Phone 999 if sudden breathlessness or chest pain with leg symptoms.

Deep vein thrombosis (DVT) — leg clots and PE risk

Deep vein thrombosis is a blood clot (thrombus) in a deep vein — usually leg (iliac, femoral, popliteal) — sometimes arm (PICC lines).

Pulmonary embolism (PE) — clot embolises to lungs — potentially fatal — 15% of untreated symptomatic DVTs may PE.

Annual UK incidence ~1 per 1,000 — hospital-associated common.

Symptoms of DVT

Classic unilateral leg:

  • swelling — calf or whole leg
  • pain — especially calf — Homan’s sign unreliable
  • warmth, erythema
  • distended superficial veins

May be subtle — clinically silent DVT — high suspicion with risk factors.

Bilateral leg swelling — think heart failure, ** lymphoedema** — less typical isolated DVT.

Pulmonary embolism — emergency

Symptoms:

  • sudden breathlessness
  • pleuritic chest pain — worse breathing in
  • tachycardia
  • haemoptysis
  • syncope, hypotension — massive PE

Phone 999 — do not wait for GP.

Risk factors — Virchow triad

  • stasis — immobility, surgery, long travel, paralysis
  • endothelial injury — trauma, catheters
  • hypercoagulability — cancer, thrombophilia, OCP/HRT, pregnancy, COVID-19

Previous DVT — strongest recurrent risk.

Diagnosis

Wells score — clinical probability

D-dimer:

  • negative with low Wells — excludes DVT
  • positive — non-specific — needs scan

Compression ultrasound — gold standard leg DVT

PE suspected:

  • CTPA chest
  • V/Q scan if contrast contraindicated

Treatment

Anticoagulation

DOACs (direct oral anticoagulants) — first-line outpatient for many:

  • apixaban
  • rivaroxaban
  • edoxaban

LMWH → warfarin — still used — INR monitoring

Minimum 3 months — provoked DVT (clear temporary trigger)

Unprovoked — extend — lifelong if high bleed risk acceptable — specialist

Severe PE

  • ** thrombolysis** — massive PE with haemodynamic compromise
  • IV heparin

Compression stockings — not routine all DVT now — PTS prevention selected cases.

Prevention

Hospital patients — LMWH, TED stockings, early mobilisation

High-risk travel:

  • move legs, hydrate
  • avoid excess alcohol
  • compression stockings if prior DVT

OCP — lowest oestrogen pill if thrombosis risk factors — see contraceptive pill — risk discussion.

Cancer-associated thrombosis

Unprovoked DVT — age-appropriate cancer screen — occult malignancy association.

Treat minimum 6 months — often indefinite if active cancer.

Do not

  • massage suspected DVT leg — PE risk
  • ignore mild calf pain after immobilisation

One swollen leg + breathlessness — 999 first — anticoagulation saves lives when started promptly.

Common questions

What are the symptoms of a blood clot in the leg?
Pain, swelling, warmth, and redness in calf or thigh — usually one leg. Veins may look more prominent. Some DVTs cause minimal symptoms — high index of suspicion with risk factors. Calf pain like cramp that does not resolve — get checked.
What is pulmonary embolism?
Blood clot travels to lungs — sudden breathlessness, sharp chest pain worse on deep breath, rapid heart rate, cough sometimes blood-streaked, feeling faint. Large PE causes collapse and death — emergency treatment with anticoagulants and sometimes clot-busting drugs.
How is DVT diagnosed?
GP calculates Wells score for probability. D-dimer blood test — if low with low Wells score, DVT unlikely. Ultrasound compression scan of leg veins confirms DVT — first-line imaging. CT pulmonary angiography if PE suspected.
How long do you take blood thinners for DVT?
Minimum 3 months for provoked DVT (clear trigger like surgery). Unprovoked or recurrent clots — often 6 months or lifelong anticoagulation after specialist review. DOACs (apixaban, rivaroxaban, edoxaban) most common — daily tablets without routine monitoring.
Can flying cause DVT?
Long-haul immobility increases risk modestly — stay hydrated, walk aisle, calf exercises, compression stockings if high risk. Combined oral contraceptive and recent surgery increase risk further — medical advice before travel.
What increases DVT risk?
Surgery, hospital admission, cancer, pregnancy and postpartum, combined contraceptive pill and HRT, obesity, immobility, previous DVT, thrombophilia, inflammatory conditions, long travel. COVID-19 infection also associated with increased clotting risk.

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