Validation of the Canadian clinical probability model for acute venous thrombosis

Objective: To validate the predictive value of the Canadian clinical probability model for acute venous thrombosis, which, to the best of the authors' knowledge, has not been done in emergency department (ED) settings outside of Canada. Methods: Demographic and clinical information, rapid D-dimer testing, and venous ultrasound imaging were obtained among patients presenting with clinically suspected venous thrombosis at a university-affiliated ED. A diagnosis of deep venous thrombosis (DVT) was made based on venous ultrasound test results or objectively documented venous thromboembolism during a 12-week follow-up period. The probability of venous thrombosis was calculated using the Canadian clinical probability model. Results: Among 102 patients, 17 (17%) were diagnosed as having venous thrombosis initially or during the three-month follow-up period. The frequency of venous thrombosis among patients categorized as having high probability was 10 of 17 [59%, 95% confidence interval (95% CI) = 35% to 82%], 6 of 44 (14%, 95% CI = 4% to 24%) with intermediate probability, and 1 of 41 (2%, 95% CI = 0.1% to 11%) with low probability. This compares with respective values of 49%, 14%, and 3%, reported by Canadian researchers in an ED study. Forty-one of 102 (40%) patients had an alternate diagnosis as likely or more likely than venous thrombosis, but only three (7%, 95% CI = 2% to 18%) of these had venous thrombosis. Conclusions: Use of the Canadian probability model for DVT in this ED resulted in effective risk stratification, comparable to previously published results.