A Tale of Two D-Dimers: Comparison of Two Assay Methods to Evaluate Deep Vein Thrombosis or Pulmonary Embolism

D-dimer testing rules out deep vein thrombosis (DVT) and pulmonary embolism (PE) in low-risk emergency department (ED) patients. Most research has measured fibrin-equivalent units (FEUs), however, many laboratories measure D-dimer units (DDUs).

Our aim was to determine whether either DDU measurements or FEU measurements can rule out DVT/PE using traditional or age-related cutoff values.

We performed a de-identified multicenter retrospective evaluation of D-dimer in nonpregnant adult ED patients to evaluate for DVT/PE. DDUs were multiplied by 2 to determine equivalent FEUs prior to analysis. Sensitivity measurements for D-dimer were calculated for FEUs, DDUs, combined FEU/DDUs, and multiple age-adjusted values.

We identified 47,088 ED patients with a D-dimer laboratory value (27,307 FEUs/19,781 DDUs) and 1623 DVT/PEs. The median combined FEU/DDU D-dimer was 400 ng/mL FEUs (interquartile range [IQR] 300-900 ng/mL FEUs) for patients without a DVT/PE vs 2530 ng/mL FEU (IQR 1094-6000 ng/mL FEUs) with a DVT/PE (p < 0.001), overall sensitivity of 87.3% (95% confidence interval [CI] 87.0-87.6%) and negative predictive value of 99.3% (95% CI 99.2-99.4%). Individually, FEUs performed better than DDUs, with sensitivities of 88.0% (95% CI 85.8-89.9%) and 86.1% (95% CI 83.1-88.7%), respectively; however, this difference was not statistically significant. Combined age-adjusted performance had a sensitivity of 90.3% (95% CI 88.3-92.0%); however, a new DDU-only age-adjusted criteria had the highest sensitivity of 91.1% (95% CI 87.9-93.6%).

Our undifferentiated D-dimer measurements had a slightly lower sensitivity to rule out DVT/PE than reported previously. Our data support using either DDU or FEU measurements for all ages or when using various age-adjusted criteria to rule out DVT/PE.