P039: Utilization of serum D-dimer assays and computed tomography pulmonary angiography (CTPA) scans in the diagnosis of pulmonary embolism among emergency department (ED) physicians

Abstract

Introduction: As the availability of Computed Tomography Pulmonary Angiography (CTPA) to rule out pulmonary embolism (PE) increases, so too does its utilization, and consequent overutilization. A variety of evidence-based algorithms and decision rules using clinical criteria and D-Dimer testing have been proposed as instruments to allow physicians to safely rule out a PE in low-risk patients. However, studies have shown mixed results with respect to both physician uptake of these decision rules and their impact on improving ordering practices among physicians. The objective of this study is to describe the prevalence of D-Dimer utilization among ED physicians and its impact on positive yield rates of CTPAs in a community setting. Methods: Data was collected on all CTPA studies ordered by ED physicians at two very high-volume community hospitals and an affiliated urgent care centre during the 2-year period between January 1, 2016 and December 31, 2017. For each CTPA, we determined if 1) a D-Dimer had been ordered prior to CTPA, if 2) the D-Dimer was positive, and if 3) the CTPA was positive for a PE. Using a chi-square test, we compared the diagnostic yield for those patients who had a D-Dimer prior to their CTPA and those who did not. Results: A total of 2,811 CTPAs were included in the analysis. Of these, 964 CTPAs (34.3%) were ordered without a D-Dimer. Of those 1,847 patients who underwent D-Dimer testing prior to the CTPA, 343 (18.7%) underwent a CTPA despite a negative D-Dimer. When compared as a group, those CTPAs preceded by a D-Dimer showed no significant difference in positive yields when compared to those CTPAs ordered without a prior D-Dimer (9.9% versus 11.3%, p = 0.26). Conclusion: The findings of this study present a complicated picture of the impact of D-Dimer utilization on CTPA ordering patterns. There is evidence of suboptimal uptake of routine D-Dimer ordering, and adherence to guidelines in terms of forgoing CTPAs in low-risk patients with negative D-Dimers. While this study design leaves unanswered the question of how many CTPAs were avoided as a result of a negative D-Dimer, the finding of a similar positive yield among those patients who had a D-Dimer ordered versus those who did not is interesting, and illustrative of the issues arising from the high false-positive rates associated with D-Dimer screening.