Deep Vein Thrombosis (DVT)
A blood clot in a deep vein — usually the leg — that can break off and cause pulmonary embolism.
Overview
DVT is a blood clot (thrombus) that forms in a deep vein, most commonly in the calf or thigh. It causes leg pain, swelling and warmth, and can lead to life-threatening pulmonary embolism if the clot travels to the lungs. Prompt anticoagulation prevents progression and recurrence.
Symptoms
- • Swelling of one leg (rarely both)
- • Calf or thigh pain or tenderness, often worse on walking
- • Warmth and redness of the affected leg
- • Distended superficial veins
Risk factors
- • Age >60
- • Obesity
- • Pregnancy and 6 weeks postpartum
- • Oestrogen-containing contraception or HRT
- • Cancer and active chemotherapy
- • Previous DVT or family history
- • Major surgery or fracture in last 3 months
Causes
- • Virchow's triad: venous stasis, endothelial injury, hypercoagulability
- • Immobility (long flights, post-surgery, hospitalisation)
- • Trauma or surgery (especially orthopaedic)
- • Cancer, pregnancy, oestrogen therapy, inherited thrombophilia
🚨 Red flags — seek urgent care
- • Sudden breathlessness, pleuritic chest pain or coughing blood — possible pulmonary embolism, call emergency services
- • Painful, cold, pale or blue leg — possible phlegmasia, emergency
- • Collapse or fainting
When to seek care
- • Unexplained leg swelling, pain or warmth — same-day assessment
- • Any breathlessness or chest pain — emergency
Diagnosis
- • Wells score to estimate pre-test probability
- • D-dimer in low-probability cases (high negative predictive value)
- • Compression duplex ultrasound is the standard confirmatory test
- • Investigate for underlying cause if unprovoked (consider cancer screening, thrombophilia)
Treatment
- • Anticoagulation — DOAC (apixaban, rivaroxaban) is first-line for most
- • LMWH preferred in pregnancy and active cancer
- • Minimum 3 months; longer or indefinite if unprovoked or high recurrence risk
- • Compression stockings for symptom control (not for prevention of post-thrombotic syndrome)
- • Thrombolysis or thrombectomy reserved for limb-threatening clots
Prevention
- • Early mobilisation after surgery
- • Mechanical and pharmacological prophylaxis in hospital
- • Hydration and calf exercises on long journeys
- • Avoid oestrogen-containing contraception in high-risk individuals
Complications
- • Pulmonary embolism (potentially fatal)
- • Post-thrombotic syndrome (chronic leg pain, swelling, ulceration)
- • Recurrent thromboembolism
- • Bleeding from anticoagulation
Prognosis
With prompt anticoagulation, most clots resolve and recurrence is uncommon during treatment. Long-term risk of post-thrombotic syndrome is 20–40%; recurrence after stopping treatment is higher in unprovoked DVT.
Education & self-care
DVT is treatable and most people recover fully with timely anticoagulation. Any new breathlessness or chest pain after a DVT is an emergency.
Frequently asked questions
Can I fly after a DVT?
Generally avoid long-haul flights for 4 weeks after diagnosis; thereafter use compression stockings, hydrate and move regularly.
Will the clot dissolve?
Anticoagulation prevents new clot; the body breaks down existing clot over weeks to months.
How long will I need anticoagulation?
Usually 3 months for a provoked DVT and at least 3–6 months — often longer — for unprovoked or recurrent clots. Cancer-associated DVT is anticoagulated for as long as the cancer is active.
Can I fly after a DVT?
Short-haul flights are generally safe once anticoagulation is established. For long-haul travel, walk regularly, hydrate, wear graduated compression stockings, and avoid alcohol and sedatives.
What is post-thrombotic syndrome?
Chronic leg swelling, aching and skin changes after a DVT, affecting up to a third of patients. Early use of graduated compression stockings and prompt anticoagulation reduce the risk.