Improving D-dimer Positive Predictive Value for Outpatients with Suspected Deep Vein Thrombosis.

CONTEXT Sensitive D-dimer assays have been developed to exclude the diagnosis of deep vein thrombosis (DVT) and have exhibited great success when used in conjunction with a diagnostic algorithm, including pre-test probability scoring and a compression ultrasound (CUS). Improving specificity of D-dimer assays would significantly improve the utility of CUSs. OBJECTIVE Our objective was to evaluate the ability of a new D-dimer assay to improve specificity, positive predictive ability, and Bayesian probability when compared with an assay previously used in our laboratory. METHODS We retrospectively reviewed 1015 continuous patients with suspected DVT. All patients were clinically evaluated in our laboratory with a D-dimer assay: 503 were clinically evaluated with a bioMérieux D-dimer test system and 512 were evaluated with a Trinity Biotech D-dimer test system. Outcomes were assessed statistically using sensitivity, negative predictive value, Bayesian negative probability, specificity, positive predictive value, and Bayesian positive probability. RESULTS The data for our study showed that with the Trinity Biotech D-dimer assay, specificity increased from 41.3% to 66.9%, positive predictive value increased 2.3 times from 8.8% to 20.0%, and the probability of DVT after positive results on a D-dimer test increased from 25% to 38% when compared with the bioMérieux D-dimer test system. In addition to the improved parameters for clinical performance, a significant number of unneeded CUSs were saved. The number of false positive D-dimer assays significantly decreased and positive predictive ability improved when the Trinity Biotech test system was used in our laboratory.