Why DVT Is Examined
Deep vein thrombosis affects approximately 1 in 1,000 adults annually in the UK. It is examined in OSCEs as a history-taking station (unilateral leg swelling), clinical assessment (applying the Wells score), prescribing (anticoagulation choice and duration), and communication (counselling on warfarin or DOACs). Its close relationship with pulmonary embolism makes it clinically urgent — 50% of untreated proximal DVTs embolise.
Anatomical Classification
| Type | Vessels | Risk of PE | Significance |
|---|---|---|---|
| Distal (calf) DVT | Tibial, peroneal, muscular veins — below popliteal | Low (1-3%) | Anticoagulate if symptomatic; serial USS if managed conservatively |
| Proximal DVT | Popliteal, femoral, iliac veins — above popliteal | High (up to 50% if untreated) | Always anticoagulate |
| Iliofemoral DVT | Iliac and femoral | Very high | May require catheter-directed thrombolysis |
Wells DVT Score — Pre-test Probability
| Clinical feature | Points |
|---|---|
| Active cancer (treatment ongoing, within 6 months, or palliative) | 1 |
| Paralysis, paresis, or recent plaster immobilisation of lower limb | 1 |
| Recently bedridden for 3 or more days, or major surgery within 12 weeks | 1 |
| Localised tenderness along deep venous system | 1 |
| Entire leg swollen | 1 |
| Calf swelling more than 3 cm greater than asymptomatic side (measured 10 cm below tibial tuberosity) | 1 |
| Pitting oedema confined to symptomatic leg | 1 |
| Collateral superficial veins (non-varicose) | 1 |
| Previously documented DVT | 1 |
| Alternative diagnosis at least as likely as DVT | -2 |
| Score | Probability |
|---|---|
| 2 or above | DVT likely — arrange compression USS directly |
| 1 or below | DVT unlikely — check D-dimer first |
Investigation Pathway
DVT unlikely (Wells 1 or below):
- D-dimer: if negative → DVT excluded; if positive → compression USS
DVT likely (Wells 2 or above):
- Compression USS directly — do not delay for D-dimer
- If USS negative but clinical suspicion remains: repeat USS in 6-8 days or MR venography
💎 Clinical Pearl
Compression USS is the gold standard. The test is positive if the vein does not collapse fully under probe pressure. Sensitivity for proximal DVT: 97%. Sensitivity for distal DVT: 73-93%. A negative proximal USS in a high-suspicion patient should be followed up with a repeat USS at 1 week to catch propagating distal clots.
DVT vs Cellulitis — Differentiation
This distinction is clinically important and frequently tested:
| Feature | DVT | Cellulitis |
|---|---|---|
| Skin warmth | Mild | Marked |
| Skin erythema | Absent or faint | Present — spreading, well-demarcated |
| Tenderness | Along deep vein | Superficial skin |
| Systemic features | Absent | Fever, raised CRP/WCC |
| Entry wound | Absent | Often present (tinea pedis, wound) |
| Pitting oedema | Present | May be present |
⚠️ Red Flag
Both can coexist — cellulitis can cause localised inflammation that mimics DVT and can also trigger a DVT. Always investigate with USS in the presence of leg swelling + tenderness, even if cellulitis seems the primary diagnosis.
Anticoagulation — NICE 2023
Proximal DVT: anticoagulate for 3-6 months
First-line: DOAC
| Drug | Dose |
|---|---|
| Apixaban | 10 mg BD x 7 days, then 5 mg BD |
| Rivaroxaban | 15 mg BD x 21 days, then 20 mg OD |
| Edoxaban | 60 mg OD after 5 days LMWH lead-in |
Special situations:
- Pregnancy: LMWH (DOACs are teratogenic — contraindicated)
- Active cancer: DOAC (rivaroxaban or edoxaban) now preferred over LMWH
- Renal impairment (eGFR below 15): LMWH preferred
- Antiphospholipid syndrome: warfarin (target INR 2.5-3.5 for recurrent VTE)
Duration:
- First provoked DVT (reversible trigger): 3 months
- Unprovoked DVT: 3-6 months minimum; discuss extended therapy (indefinite) based on bleeding vs recurrence risk
- Cancer-associated DVT: treat until cancer in remission + 3 months beyond
VTE Prophylaxis — Hospital Inpatients
All patients admitted to hospital must be risk-assessed for VTE on admission.
| Patient group | Prophylaxis |
|---|---|
| Medical inpatients at risk | LMWH (enoxaparin 40 mg OD SC) |
| Surgical patients at risk | LMWH + anti-embolism stockings (TED stockings) |
| Contraindication to LMWH (active bleeding, thrombocytopaenia) | Mechanical compression device (pneumatic calf compression) |
LMWH should be started preoperatively (the evening before elective surgery) and continued for 28 days after major orthopaedic procedures and at least 10 days after other major surgery.
Frequently Asked Questions
"What is the most common cause of a provoked DVT?"
Surgery (particularly orthopaedic — hip and knee replacement) and prolonged immobility are the most common causes of provoked DVT in the UK. Other provoking factors: long-haul travel (economy class syndrome), hospitalisation, trauma, pregnancy and the puerperium, combined oral contraceptive pill, HRT, and acute medical illness. A provoked DVT has a lower recurrence risk after anticoagulation is stopped compared with an unprovoked DVT.
"What inherited thrombophilias increase DVT risk?"
Factor V Leiden mutation (most common — 5% of European population), prothrombin gene mutation G20210A, protein C deficiency, protein S deficiency, antithrombin III deficiency. Testing is recommended after an unprovoked DVT in young patients, recurrent DVT, DVT in an unusual site (mesenteric, cerebral), or strong family history. Note: thrombophilia testing should be delayed until anticoagulation has been stopped for at least 4-6 weeks.
"How does the combined oral contraceptive pill increase DVT risk?"
Oestrogen in the COCP increases hepatic production of clotting factors (II, VII, VIII, X) and reduces anticoagulant proteins C and S, shifting the coagulation balance towards thrombosis. The absolute risk is small (3-4 per 10,000 women/year on COCP vs 1-2 per 10,000 not on it) but doubles or triples with concomitant smoking, Factor V Leiden, or obesity. Progestogen-only contraceptives carry no significant VTE risk.
"When is inferior vena cava (IVC) filter insertion indicated?"
IVC filter insertion is indicated when anticoagulation is absolutely contraindicated (active major haemorrhage, recent CNS surgery, recent major trauma) and the patient has a proximal DVT or PE. It physically prevents emboli from reaching the lungs. Filters should be retrievable if possible and removed once anticoagulation becomes safe. They do not treat the underlying DVT and are associated with long-term complications including filter thrombosis and post-thrombotic syndrome.
"What is post-thrombotic syndrome?"
Post-thrombotic syndrome (PTS) is a chronic complication of DVT occurring in 20-50% of patients within 2 years. Valve damage causes venous reflux and hypertension, leading to: leg pain, heaviness, swelling, varicosities, skin changes (lipodermatosclerosis, hyperpigmentation), and in severe cases, venous ulceration. Prevention: adequate anticoagulation, compression stockings for at least 2 years after proximal DVT. Treatment: compression hosiery, venoactive drugs, wound care for ulcers.
Related Posts
- Pulmonary Embolism OSCE — DVT as the precursor to PE in the VTE spectrum
- Peripheral Vascular Examination OSCE — assessing the leg for DVT and arterial disease
- Medication Review OSCE — reviewing anticoagulation and VTE prophylaxis on the ward