Deep venous thrombosis: Withholding anticoagulation therapy after negative complete lower limb US findings

PURPOSE: To establish the safety of withholding anticoagulation therapy after negative findings at a complete lower limb ultrasonographic (US) examination of the symptomatic leg for suspected deep venous thrombosis (DVT). MATERIALS AND METHODS: Regional ethics committee approval and patient consent were obtained. A total of 542 consecutive ambulatory patients presented to the emergency department and were prospectively recruited from April 2001 to May 2003. Of these patients, 16 were excluded, and radiology residents and sonographers performed a complete lower limb US examination by means of compression and Doppler US in 526 patients. Patients with negative US findings received no anticoagulation therapy, and they were observed for occurrence of any thromboembolic event for 3 months. Patients with progressive or new symptoms that were indicative of thromboembolism within the follow-up period underwent objective testing with US, computed tomographic (CT) pulmonary angiography, or both. RESULTS: There were 413 patients (78.5%) with US findings that were negative for DVT and 113 patients (21.5%) with findings that were positive. There were 64 patients (56.6%) with DVT isolated to the calf and 49 (43.4%) with proximal DVT. Of the 413 patients with negative initial US findings, 16 (3.9%) underwent a second US examination for new or progressive symptoms of DVT, one patient (0.25%) underwent CT pulmonary angiography for suspected pulmonary embolism, and one patient (0.25%) underwent both US and CT pulmonary angiography during the 3-month follow-up period. One of these patients (0.24%; 95% confidence interval: 0.01%, 1.3%) developed pulmonary embolism, which was diagnosed with CT pulmonary angiography. DVT was not diagnosed in any patient, and no patient died during follow-up. The negative predictive value of a complete single lower limb US examination to exclude clinically important DVT is 99.6% (95% confidence interval: 98.4%, 99.9%). CONCLUSION: A single negative complete lower limb US examination is sufficient to exclude clinically important DVT, and it is safe to withhold anticoagulation therapy after negative complete lower limb US findings were obtained in patients suspected of having symptomatic lower limb DVT. New or progressive symptoms require further objective imaging.