10. Venous Thrombosis
📄 Definition
Venous thrombosis refers to the formation of a blood clot within a vein, most commonly affecting the deep veins of the leg (DVT) and the pulmonary arteries (PE). Collectively, these are called venous thromboembolism (VTE).
🧠 Pathophysiology – Virchow’s Triad
| Factor | Example |
|---|---|
| Stasis | Immobility, surgery, long flights |
| Hypercoagulability | Pregnancy, malignancy, inherited thrombophilia |
| Endothelial Injury | Trauma, central venous catheters, surgery |
📋 Clinical Presentations
🔹 Deep Vein Thrombosis (DVT)
Unilateral leg swelling, pain, erythema
Calf tenderness or warmth
Dilated superficial veins
Positive Homan’s sign (low specificity)
🔹 Pulmonary Embolism (PE)
Dyspnoea, pleuritic chest pain
Cough ± haemoptysis
Tachycardia, tachypnoea
Hypoxia ± hypotension (massive PE)
Raised JVP (if RV strain)
Risk Factors –
Mnemonic: THROMBOSIS
Trauma or surgery (esp. orthopaedic)
Hospitalisation or immobility
Recurrent miscarriage or thrombophilia
Oestrogen (OCP, HRT, pregnancy)
Malignancy
BMI ↑ (obesity)
Older age
Smoking
Infection or inflammation (e.g. IBD)
Stroke or spinal cord injury
Investigations
🥇 First-Line
DVT:
Wells score
D-dimer (if Wells ≤1)
Proximal leg Doppler US (if Wells ≥2 or D-dimer positive)
PE:
Wells score
D-dimer (if Wells ≤4)
CTPA (if Wells >4 or D-dimer positive)
V/Q scan (if CTPA contraindicated e.g. renal failure, pregnancy)
🥈 Second-Line
ECG (sinus tachycardia, S1Q3T3 in PE)
ABG (may show hypoxia in PE)
CXR (to exclude other causes)
Thrombophilia screen (if unprovoked and <50 years old)
Wells Score for DVT (2-Level DVT Wells Score – NICE NG158)
Mnemonic: “CLOTS DVT PACT”
| Letter | Feature | Score |
|---|---|---|
| C | Cancer – Active within 6 months or palliative | +1 |
| L | Leg swollen – Entire leg swelling | +1 |
| O | Oedema – Pitting oedema confined to the symptomatic leg | +1 |
| T | Tenderness – Along deep vein system | +1 |
| S | Surgery / bedbound – Major surgery within 12 weeks or bedridden ≥3 days | +1 |
| D | Deep vein history – Previous documented DVT | +1 |
| V | Varicosities absent, but – Visible collateral veins (non-varicose) | +1 |
| T | Thigh / Calf swelling – ≥3 cm difference 10 cm below tibial tuberosity | +1 |
| P | Paralysis / paresis / plaster immobilisation of lower limb | +1 |
| A | Alternate diagnosis as likely or more likely than DVT | –2 |
| C | Count total score | — |
| T | Take next Test (D-dimer or ultrasound based on score) | — |
Interpretation:
| Total Score | Clinical Probability of DVT | Action |
|---|---|---|
| ≥2 | DVT likely | Perform proximal leg vein ultrasound within 4 hours. If delayed, do D-dimer and offer interim anticoagulation. |
| <2 | DVT unlikely | Do D-dimer test: if positive, perform ultrasound as above. |
Management – Mnemonic: ACT-VTE
Anticoagulation:
DOAC (e.g. apixaban, rivaroxaban) 1st line
LMWH if cancer or pregnancy
Duration:
3 months (provoked)
6+ months (unprovoked or ongoing risk)
Confirm diagnosis – imaging before starting anticoagulation unless haemodynamic compromise
Thrombolysis – massive PE with shock
Vena cava filter – if anticoagulation contraindicated
Treat reversible causes (e.g. immobility, cancer)
Educate – compression stockings, medication adherence
Special Considerations
Pregnancy: LMWH preferred, avoid DOACs
Cancer-associated thrombosis: Continue LMWH or DOAC long-term
Recurrent VTE: Evaluate for thrombophilia, extended anticoagulation
⚠️ Complications
Post-thrombotic syndrome
Pulmonary hypertension (chronic PE)
Recurrent VTE
Bleeding from anticoagulation
🔺 Last updated in line with NICE NG158 – Venous thromboembolic diseases: diagnosis, management and thrombophilia testing
Published: March 2020 • Last updated: May 2023
Last reviewed: August 2025
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