## Investigation of Choice for DVT Diagnosis **Key Point:** Compression ultrasonography (duplex ultrasound) is the gold standard first-line investigation for suspected DVT in clinical practice. ### Why Compression Ultrasonography? 1. **Non-invasive** — no radiation or contrast required 2. **High sensitivity and specificity** — >95% for proximal DVT (popliteal, femoral, iliac veins) 3. **Operator-dependent but reproducible** — loss of compressibility of the vein is diagnostic 4. **Real-time assessment** — can assess flow, echogenicity, and thrombus characteristics 5. **Bedside capability** — can be performed in acute settings 6. **Cost-effective** — widely available in most hospitals ### Diagnostic Criteria on Ultrasound | Finding | Significance | |---------|-------------| | Loss of vein compressibility | Diagnostic of DVT | | Absence of spontaneous flow | Suggests thrombosis | | Absence of flow augmentation | Indicates obstruction | | Echogenic material in lumen | Thrombus visualisation | | Dilated vein (>0.5 cm difference) | Supportive finding | **Clinical Pearl:** The **absence of compressibility** of the vein on ultrasound is the single most reliable sign of DVT and does not require Doppler confirmation. **High-Yield:** Compression ultrasound has largely replaced venography as the diagnostic standard because it is non-invasive, repeatable, and has excellent sensitivity for symptomatic proximal DVT. ### Timing of Investigation **Tip:** In a patient with high clinical suspicion (Wells score ≥2) and acute presentation, compression ultrasound should be performed **within 4 hours** of presentation to guide anticoagulation decisions. [cite:Bailey & Love's Short Practice of Surgery 27e Ch 56]
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