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Age-adjusted D-dimer excludes pulmonary embolism and reduces unnecessary radiation exposure in older adults: retrospective study
  1. Jennifer Nobes1,
  2. Claudia-Martina Messow2,
  3. Mohammed Khan3,
  4. Petr Hrobar4,
  5. Chris Isles1
  1. 1Medical Unit, Dumfries and Galloway Royal Infirmary, Dumfries, UK
  2. 2Robertson Centre for Biostatistics, University of Glasgow, Glasgow, UK
  3. 3Department of Haematology, Aberdeen Royal Infirmary, Aberdeen, UK
  4. 4Department of Radiology, Dumfries and Galloway Royal Infirmary, Dumfries, UK
  1. Correspondence to Professor Chris Isles, Medical Unit, Dumfries Infirmary, Dumfries DG1 4AP, UK; chris.isles{at}nhs.net

Abstract

Background Patients in whom a diagnosis of pulmonary embolism (PE) is suspected and whose D-dimers are elevated frequently require CT pulmonary angiogram (CTPA) for diagnosis. Because D-dimer rises with age, an age-adjusted D-dimer threshold may prevent unnecessary radiation exposure from CTPA in older patients.

Objective To determine the efficacy and safety of implementing an age-adjusted D-dimer threshold to exclude PE.

Design, settings and patients Retrospective comparison of conventional and age-adjusted D-dimer thresholds in 1000 consecutive patients who had both D-dimer and CTPA.

Main outcome measures Conventional and age-adjusted D-dimer thresholds for excluding PE were <250 ng/mL and 5× age for patients older than 50 years, respectively. We defined patients as unlikely to have PE using the revised Geneva score (RGS) and two different categories of clinical risk: RGS ≤5 and RGS ≤10.

Results We diagnosed PE by CTPA in 244 (24.4%) patients. 3/86 patients (3.5%) whose D-dimer was below the conventional threshold of 250 ng/mL had PE (RGS 3, 9 and 14), all of which were judged to be light clot load (group 1). 3/108 patients (2.8%) whose D-dimer lay between 250 ng/mL and the age-adjusted threshold had PE (RGS 6, 8 and 9), all of which were again judged to be light clot load (group 2). 62/108 group 2 patients with RGS ≤5 were considered unlikely to have PE as were 102/108 using the RGS clinical risk category ≤10. None of the 62 patients with RGS ≤5 had PE while 3/102 patients with RGS ≤10 had PE. 236/806 patients (29.3%) whose D-dimer was above the age-adjusted threshold had PE (group 3).

Conclusions In a consecutive series of 1000 patients, an RGS ≤5 and an age-adjusted D-dimer would have led to 62 fewer CTPA at a cost of no missed PEs.

  • Pulmonary embolism
  • D-dimer
  • Age-adjusted D-dimer
  • CTPA

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Footnotes

  • Contributors CI had the idea. JN compiled the 1000 D-dimer/CTPA pairs and undertook the first set of analyses. PH reviewed the CTPAs. C-MM performed the statistical analyses. CI wrote the first draft. All authors contributed to the final draft.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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