Safety of a single duplex scan to exclude deep venous thrombosis.

BACKGROUND Guidelines advocate that a negative ultrasonographic scan needs to be followed by venography, or a repeat scan after 1 week, to detect potentially missed calf vein thrombosis. This study aimed to evaluate whether anticoagulation can safely be withheld on the basis of a single negative duplex scan in patients presenting with suspected deep venous thrombosis (DVT). METHODS Duplex scan reports, case notes and questionnaires returned by general practitioners of patients with suspected DVT were analysed retrospectively. The main outcome measure was occurrence of an adverse thromboembolic event, a symptomatic DVT or a pulmonary embolism, within 3 months after a negative duplex scan. RESULTS Some 537 patients had 706 leg scans performed, the majority because of leg symptoms or to look for indirect evidence of pulmonary embolism. Among 352 patients, who had 429 negative leg scans, four possible adverse events were identified. The rate of adverse outcome was therefore 1.1 per cent per patient and 0.9 per cent per leg. CONCLUSION Withholding anticoagulation in patients who had a single, complete, negative duplex scan is safe. A repeat scan should be performed if there is ongoing high clinical suspicion and considered in patients in whom the calf veins could not be visualized.