Validation of the Canadian Clinical Probability Model for Acute Venous Thrombosis

Abstract

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.

Systematic review and meta-analysis of the diagnostic accuracy of ultrasonography for deep vein thrombosis

“…Studies of serial US [109-112,120], a single full-leg US [121-124], or US as part of a diagnostic algorithm [114,116,117,125-129] have shown low rates of thromboembolism during three to six month follow up. This suggests that, although our meta-analysis has shown that US does not have perfect sensitivity for DVT (especially distal thrombus), this does not translate into high rates of adverse outcome.…”

The utility of pretest probability assessment in patients with clinically suspected venous thromboembolism

“…Identification of a potential alternative diagnosis as likely or more likely than DVT, present in 40–61% of cases of suspected DVT [20,22,31,48], is a critical criterion of the Wells score, which introduces a subjective element into the assessment. If uncertainty exists about the interpretation of this item, an assumption that no alternative diagnosis exists maximizes the safety of this strategy.…”

“…If uncertainty exists about the interpretation of this item, an assumption that no alternative diagnosis exists maximizes the safety of this strategy. Nevertheless, this has since become the most widely used prediction rule for DVT, and several studies performed in different institutions [9,14,20,29–31,48–51], including clinical management studies [14,31,51], have validated the clinical utility of the simplified score in outpatients, and one management study has validated its utility in inpatients [52]. PTP was usually assessed either by the study physicians or emergency department physicians, but in one study [9], it was initially assessed by a vascular technologist or specialist nurse who could subsequently be over‐ridden by a physician, and in another was assessed by a trained nurse who then deferred to a physician, who decided on the likely presence or otherwise of an alternative diagnosis [31].…”

“… Utility of pre‐test probability assessment using modified Well's scores in patients with clinically suspected venous thromboembolism. DVT: data from 11 studies containing 3034 patients with suspected DVT [9,14,20,29–31,48–52] (2801 outpatients, 233 inpatients; prevalence of confirmed DVT: 20%). PE: Data from four studies [10,33,56,57] containing 2840 in and outpatients with suspected PE (prevalence of confirmed PE: 16.9%).…”

Review of the Evidence on Diagnosis of Deep Venous Thrombosis and Pulmonary Embolism

“…The sensitivities and specifi cities of the rule (at each cutoff) refl ect how correctly the rule predicts the presence or absence of disease. We identifi ed 19 studies that evaluated clinical prediction rules for the diagnosis of DVT, [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] and 8 studies evaluating clinical prediction rules for the diagnosis of pulmonary embolism, [35][36][37][38][39][40][41][42] although common patients were reported in 3 studies. [40][41][42] (Supplemental Appendix 1, available online at http://www.annfammed.org/cgi/content/full/5/1/63/DC1).…”