D-DIMER TESTING FOR SUSPECTED PULMONARY-EMBOLISM IN OUTPATIENTS

The plasma level of D-dimer, a fibrin degradation product (FDP), is ne arly always increased in the presence of acute pulmonary embolism (PE) . Hence, a normal D-dimer level (below a cutoff value of 500 mu g/L by enzyme-linked immunosorbent assay [ELISA]) may allow the exclusion of PE. To assess the negative predictive value of a D-dimer concentratio n below 500 mu g/L in outpatients with suspected PE, and the safety of withholding anticoagulant treatment from such patients, we performed D-dimer assays, lower limb venous compression ultrasonography, and lun g scans in 671 consecutive outpatients presenting in the Emergency Cen ter of the Geneva University Hospital with suspected PE. Pulmonary ang iography was reserved for patients with an inconclusive noninvasive wo rkup. Patients with a normal D-dimer concentration were discharged wit hout anticoagulant treatment and followed for 3 mo. The prevalence of PE was 29%, and D-dimer (using a cutoff of 500 mu g/L) had a diagnosti c sensitivity for PE of 99.5%. Overall diagnostic specificity of D-dim er was 41%, but it was lower among older patients. Of the 198 patients with a D-dimer concentration below the cutoff value, 196 were free of PE, one had a PE, and one had incomplete information because of loss to follow-up. Thus, the negative predictive value of D-dimer concentra tion fell between 197 of 198 and 196 of 198 cases of PE (99% [95% CI: 96.4 to 99.9]). Using a cutoff value of 4,000 mu g/L, the overall spec ificity of D-dimer concentration for PE was 93.1%. In conclusion, a pl asma D-dimer concentration below 500 mu g/L allows the exclusion of PE in 29% of outpatients suspected of having PE. Withholding anticoagula tion from such patients is associated with a conservative 1% risk of t hromboembolic events during follow-up.