A simplified decision rule to rule out deep vein thrombosis using clinical assessment and D-dimer

Current clinical decision rules to exclude deep vein thrombosis (DVT) are underused partly because of their complexity. A simplified rule that can be easily applied would be more appealing to use in clinical practice.

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 (CI) of DVT prevalence was <2%.

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 pretest 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% 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).

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.