A 28-year-old woman on combined oral contraceptive pills (COCPs) for 6 months presents with sudden onset severe unilateral leg pain, swelling, and warmth. She has no prior history of thromboembolism. What is the most appropriate investigation to confirm the suspected diagnosis?

Explanation

## Clinical Scenario Analysis The patient presents with classic signs of deep vein thrombosis (DVT): unilateral leg pain, swelling, and warmth. COCPs are a known risk factor for venous thromboembolism (VTE), particularly in the first year of use. ## Investigation of Choice for DVT **Key Point:** Compression ultrasonography (B-mode ultrasound with compression) is the gold standard first-line investigation for suspected DVT of the lower limb. ### Why Compression Ultrasonography? 1. **High sensitivity and specificity**: ≥95% for proximal DVT (popliteal and femoral veins) 2. **Non-invasive**: No radiation, no contrast required 3. **Readily available**: Can be performed at bedside or in outpatient setting 4. **Cost-effective**: Cheaper than CT or MRI 5. **Safe in pregnancy**: Important consideration in reproductive-age women ## Comparison of Investigations | Investigation | Sensitivity | Specificity | Use | Limitation | |---|---|---|---|---| | **Compression US** | >95% (proximal) | >95% | First-line for DVT | Less sensitive for calf veins | | D-dimer | >95% | 40% | Rule-out (high NPV) | High false positives; not confirmatory | | Doppler US | 90–95% | 95% | Adjunct to compression US | Operator-dependent | | CT angiography | 95% | 98% | PE suspected; IVC thrombus | Radiation; contrast; expensive | **High-Yield:** Compression ultrasonography is the investigation of choice for DVT because it directly visualizes the thrombus and assesses compressibility of the vein. ## Clinical Pearl In a patient on COCPs with acute DVT, investigation should be **urgent** (within 24 hours). After confirmation, the COCP must be stopped immediately and anticoagulation initiated. Thrombophilia screening (Factor V Leiden, prothrombin mutation, antithrombin, protein C/S) may be considered after acute phase management. ## COCP and VTE Risk **Key Point:** Combined oral contraceptives increase VTE risk 3–4 fold compared to non-users. Risk is highest in the first year of use and with third/fourth-generation progestins (desogestrel, gestodene). [cite:Park 26e Ch 3]