Deep Vein Thrombosis (DVT) — Blood Clots in the Leg
Deep vein thrombosis (DVT) is the formation of a blood clot (thrombus) in one of the deep veins — most commonly the veins of the calf, thigh, or pelvis. DVT can cause local pain and swelling, but its most serious complication is pulmonary embolism — when a fragment of the clot breaks off and travels to the lungs, potentially causing a life-threatening blockage. DVT and pulmonary embolism are collectively called venous thromboembolism (VTE).
Risk factors
- Prolonged immobility — long-haul flights (economy class syndrome), bed rest after surgery or illness, paralysis
- Recent surgery — particularly orthopaedic (hip or knee replacement), abdominal, or pelvic surgery
- Active malignancy — cancer increases clot risk through pro-coagulant mechanisms
- Pregnancy and postpartum period — elevated oestrogen and venous stasis increase thrombosis risk
- Combined oral contraceptive pill — particularly high-oestrogen formulations
- Inherited thrombophilia — Factor V Leiden, prothrombin gene mutation, protein C/S deficiency — conditions that increase clotting tendency
- Prior DVT or PE — recurrence risk is significantly elevated
- Obesity, dehydration, varicose veins
Symptoms
- Calf or thigh pain — often aching, cramping, or throbbing
- Swelling of the affected leg — asymmetric oedema
- Redness and warmth of the skin over the affected vein
- Dilated superficial veins
- Homan's sign — pain on dorsiflexion of the foot — unreliable but classically taught
Many DVTs are silent
A significant proportion of DVTs cause no symptoms at all — the clot is discovered incidentally during imaging for another purpose, or first presents as pulmonary embolism without preceding leg symptoms.
Diagnosis
- D-dimer blood test — highly sensitive for VTE. A negative D-dimer in a low-probability patient effectively rules out DVT. An elevated D-dimer requires further imaging.
- Compression duplex ultrasound — the gold standard for DVT diagnosis. Non-invasive, rapid, and highly accurate for proximal DVT. The affected vein is non-compressible when the clot is present.
- CT venography — used when duplex ultrasound is inconclusive or when iliac or inferior vena cava thrombus is suspected.