Raising the D-dimer threshold for ruling out pulmonary embolism: A single-site, observational study with a historical comparison.

Objective: The objective of this study was to assess the impact of introduction of a new pulmonary embolism (PE) diagnostic guideline with a raised D-dimer threshold.

Methods: This is a single-site, observational, cohort study with a historical comparison. The new guideline raised the D-dimer threshold to 1000 ng/mL for most patients with a Wells' score of 4 or less. Patients investigated for PE with a D-dimer level and/or definitive imaging in 6-month periods before and after the introduction of the guideline were eligible. Patients with D-dimers of 500-1000 ng/mL were prospectively followed up at 3 months for missed PE.

Results: During the pre-intervention period, 688 patients were investigated for PE, 366 (53.2%) received definitive imaging and 39 PE were diagnosed (5.7% overall, 10.7% of those imaged). For the 121 patients with D-dimers ≥500 and <1000 ng/mL, 87 (71.9%) were imaged with 7 (5.8%) having a PE diagnosed. Post intervention there were 930 patients, of which 426 (45.8%) received definitive chest imaging and there were 50 patients with PE diagnosed (5.4% overall, 11.7% of those imaged). For the 185 patients with D-dimers ≥500 and <1000 ng/mL, 60 (32.4%) were imaged with 5 (2.7%) having PE diagnosed. No cases of missed PE were identified at 3 months.

Conclusion: The introduction of the new guideline was associated with a reduction in overall imaging rates without evidence of missed PE. Further evaluation in other settings is recommended.