A Simplified Decision Rule to Rule Out Deep Vein Thrombosis Using Clinical Assessment And D‐dimer
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BACKGROUND: Current clinical decision rules to exclude deep vein thrombosis (DVT) are underutilized partly because of their complexity. A simplified rule that can be easily applied would be more appealing to use in clinical practice. METHODS: We used individual patient data from prospective diagnostic studies of patients suspected of DVT to develop a new clinical decision rule. The primary outcome was presence of DVT either at initial testing or during follow-up. DVT was considered safely excluded if the upper 95% confidence interval of DVT prevalence was < 2%. RESULTS: Four studies and 3368 patients were eligible for this analysis. Overall prevalence of DVT was 17%. In addition to D-dimer, two variables, calf swelling and DVT as the most likely diagnosis are included in the new rule. Based on these two variables, two clinical pre-test probability (CPTP) groups were defined; low (none of the two items present) and high (at least one of the items present). DVT can be safely excluded in patients with low CPTP with a D-dimer < 500 ng/mL (prevalence = 0.1%; 95% confidence interval (CI) = 0.0%, 0.8%), low CPTP with a D-dimer between 500 ng/mL and 1000 ng/mL (prevalence = 0.3%; 95% CI = 0.0%, 1.7%), and D-dimer < 500 ng/mL in patients with high CPTP (prevalence = 0.3%; 95% CI = 0.0%, 1.0%). CONCLUSIONS: The combination of D-dimer and Wells items resulted in a simple clinical decision rule with 3 items. The results suggest that the rule can safely exclude DVT. Prospective validation is required.
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