About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
The Bottom Line
- DVT: thrombus in deep vein (usually iliac, femoral, popliteal) — risk of propagation to PE
- Wells score for DVT: ≤1 unlikely → D-dimer; ≥2 likely → compression USS within 4 h
- Proximal DVT (above knee): higher risk of PE than distal (calf) DVT
- Treatment: DOAC first-line (apixaban or rivaroxaban) — can start immediately without LMWH bridge
- Duration: provoked (transient risk factor) = 3 months; unprovoked = ≥3 months, consider indefinite
Overview
Deep vein thrombosis is the formation of a blood clot in a deep vein, most commonly in the lower extremities (iliac, femoral, or popliteal veins). It constitutes, together with pulmonary embolism, the spectrum of venous thromboembolism (VTE). The pathogenesis reflects Virchow's triad: venous stasis, endothelial injury, and hypercoagulability. Proximal DVT (above the knee) carries a significantly higher risk of pulmonary embolism than distal (calf vein) DVT.
Epidemiology
Annual incidence of DVT is approximately 1–2 per 1,000 adults. VTE is the third most common cardiovascular disease. Risk factors include: immobilisation, recent surgery (especially orthopaedic), malignancy, combined oral contraceptive/HRT, pregnancy, obesity, long-haul travel (>4 hours), previous VTE, thrombophilia (factor V Leiden, prothrombin gene mutation, antiphospholipid syndrome), and active inflammatory conditions. Hospital-acquired VTE is a major cause of preventable death — VTE risk assessment on all admissions is mandatory.
Clinical Features
Symptoms
Unilateral leg swelling — the most common symptom
Leg pain — often calf, worse on walking
Warmth and redness of the affected limb
May be asymptomatic — PE may be the first presentation
Signs
Unilateral pitting oedema
Calf tenderness — often along the course of the deep veins
Increased calf circumference (>3 cm difference vs contralateral limb)
Warmth and erythema
Dilated superficial collateral veins
Homans sign (calf pain on dorsiflexion) — unreliable, NOT recommended as diagnostic test
Phlegmasia cerulea dolens: massive ilio-femoral DVT with cyanosis and vascular compromise
Investigations
First-line
Two-level Wells score for DVTCalculates clinical probability. ≤1 = unlikely → D-dimer; ≥2 = likely → proximal leg vein compression USS
D-dimerOnly if Wells ≤1. Negative D-dimer effectively excludes DVT (high sensitivity). Positive D-dimer is non-specific — requires USS
Second-line
Compression USSGold standard imaging. Non-compressible vein = DVT. If initially negative and D-dimer positive → repeat USS in 6–8 days
BloodsFBC, U&Es, LFTs, coagulation screen (baseline before anticoagulation)
Specialist
CT/MR venographyIf USS inconclusive or iliac vein/IVC thrombosis suspected
Thrombophilia screenOnly if unprovoked VTE in young patient (<50), recurrent VTE, or strong family history. Check ≥3 months after event and off anticoagulation
Cancer screenConsider in unprovoked DVT: CT chest/abdomen/pelvis, FBC, calcium, LFTs, urinalysis — malignancy present in ~10%
Management
NICE NG158 (VTE), updated 20231
Anticoagulation — start immediately if DVT likely (Wells ≥2)
- DOAC first-line: apixaban 10 mg BD for 7 days then 5 mg BD; or rivaroxaban 15 mg BD for 21 days then 20 mg OD
- DOACs do NOT require LMWH bridging — can be started immediately
- Alternative: LMWH bridging to warfarin (if DOAC contraindicated e.g. renal failure, antiphospholipid syndrome)
2
Duration of anticoagulation
- Provoked DVT (transient risk factor: surgery, immobilisation, COCP): 3 months
- Unprovoked DVT: minimum 3 months, then assess for indefinite anticoagulation (balance bleeding risk vs recurrence)
- Cancer-associated DVT: DOAC (apixaban or edoxaban) or LMWH for ≥6 months; continue while cancer active
- Recurrent VTE: indefinite anticoagulation
3
Supportive measures
- Early mobilisation (bed rest is NOT recommended)
- Compression stockings are NO LONGER routinely recommended for prevention of post-thrombotic syndrome (NICE 2020 update)
- Elevate the limb for comfort
4
IVC filter
- Only if anticoagulation is absolutely contraindicated (e.g. active major bleeding) and proximal DVT/PE present
- Retrievable filters preferred — remove as soon as anticoagulation can be safely started
Complications
- Pulmonary embolism: Most feared acute complication — ~50% of untreated proximal DVTs embolise
- Post-thrombotic syndrome: Chronic venous insufficiency (pain, swelling, skin changes, ulceration) affecting 20–50% after DVT
- Recurrence: ~5% per year for unprovoked VTE if anticoagulation stopped
- Phlegmasia cerulea dolens: Massive DVT with venous gangrene — surgical emergency
- Anticoagulation-related bleeding: GI bleed, intracranial haemorrhage
UKMLA Exam Tips
- 1Wells DVT: ≤1 = unlikely → D-dimer. ≥2 = likely → USS. Same logic as PE but different scores
- 2DOACs (apixaban, rivaroxaban) are first-line for DVT — no LMWH bridge needed. This is the key change from older practice
- 3Provoked = 3 months. Unprovoked = consider indefinite. Cancer = continue while active
- 4In pregnancy: LMWH is first-line (DOACs and warfarin are contraindicated)
- 5Compression stockings no longer routinely recommended for post-thrombotic syndrome prevention (changed in 2020)
- 6Unprovoked DVT in >40 years: consider cancer screen — CT CAP, FBC, calcium, LFTs
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