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


Craig M Nelson, PhD, CLS; Geary S Wright, BA, MLT; Tom R Silbaugh, CPT; Louis J Cota, CLS

Winter 2009 - Volume 13 Number 1


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 pretest 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.


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