Retrospective Evaluation of the D-Dimer in Patients Undergoing CTPA for PE Evaluation

Computed tomography pulmonary angiogram (CTPA) is the choice imaging modality for diagnosis of pulmonary embolism (PE). Studies have demonstrated more appropriate use of CTPA following implementation of the Wells or Revised Geneva scores and/or D-dimer level thresholds into clinical frameworks. During the study period, these measures were not required prior to ordering a CTPA at our institution. The aim of this study was to retrospectively evaluate the institutional utilization and ordering patterns preceding CTPA for evaluation of PE, with focus on the laboratory D-dimer test.

This retrospective chart review included patients that underwent CTPA for suspected PE between January 1, 2022 and December 31, 2022. Data included clinical factors, D-dimer levels, CTPA results, and subspecialty of ordering providers. Statistical analyses were performed via SAS v9.4. P values < 0.05 were considered statistically significant.

A total of 660 patients were included in this study, with 54 positives for PE (8.2%). The D-dimer was ordered for 332 patients, and elevated ( ≥ 500 ng/mL) in 20 patients with, and 299 without PE. When analyzed using the institutional threshold as a binary (elevated vs non-elevated), D-dimer levels were not associated with PE on CTPA (p = 0.2099). However, when analyzed as a continuous variable using the standard and age-adjusted thresholds, greater values were associated with PE (p < 0.05). Patients with retrospective high-risk Wells or Revised Geneva scores were more likely to proceed directly to CTPA.

When analyzed as a continuous variable, elevated D-dimer levels were associated with PE. Our findings also suggest that the D-dimer is more widely used in the diagnostic workup in those at low risk of PE, likely in a "rule out" manner. Future work should evaluate D-dimer utilization, laboratory levels, and clinical probability scores of those with suspected PE in groups that did and did not undergo CTPA.