The standard diagnostic approach in patients with suspected deep vein thrombosis is to repeat the compression ultrasonography after 1 week in all patients with an initial normal result. We hypothesized that a normal finding of a D-dimer assay safely obviates the need for repeated ultrasonography. In addition, we evaluated the potential value of a pretest probability assessment for this purpose.
At presentation, consecutive outpatients with suspected thrombosis underwent independent assessment by means of ultrasonography of the proximal veins, a whole-blood D-dimer assay, and a pretest clinical model. Patients with normal ultrasonographic findings and an abnormal D-dimer assay result were scheduled for repeated ultrasonography. We evaluated the incidence of symptomatic venous thromboembolic complications during a 3-month follow-up, and the value of clinical pretest probability with ultrasonography or D-dimer assay in scenario analyses.
We studied 1756 patients with prevalence of thrombosis of 22%. At entry, results of the D-dimer assay and ultrasonography were normal in 828 patients (47%). Of these, 6 returned with confirmed symptomatic venous thromboembolism (complication rate, 0.7%; 95% confidence interval [CI], 0.3%-1.6%). Repeated ultrasonography was avoided in 61% of the patients with an initial normal test result. Scenario analyses disclosed that the complication rate was 1.6% (95% CI, 0.8%-2.6%) in those with a low clinical pretest probability and a normal result of ultrasonography at referral, whereas this figure was 1.8% (95% CI, 0.9%-3.3%) in patients with a low clinical probability result and a normal result of the D-dimer assay at referral.
It is safe to withhold repeated ultrasonography in patients with suspected deep vein thrombosis who have normal results of ultrasonograpy and the SimpliRED D-dimer assay at presentation. The combination of a low clinical pretest probability with a normal result of compression ultrasonography or the D-dimer assay appears to be equally safe in refuting the diagnosis of deep vein thrombosis.