title: Age-adjusted D-dimer excludes pulmonary embolism and reduces unnecessary radiation exposure in older adults: retrospective study.
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.
  Retrospective comparison of conventional and age-adjusted D-dimer thresholds in 1000 consecutive patients who had both D-dimer and CTPA.
  
  
  METHODS
  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.
authors.affiliation: Medical Unit, Dumfries and Galloway Royal Infirmary, Dumfries, UK.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Nobes
authors.affiliation: Robertson Centre for Biostatistics, University of Glasgow, Glasgow, UK.
authors.forename: Claudia-Martina
authors.initials: CM
authors.lastname: Messow
authors.affiliation: Department of Haematology, Aberdeen Royal Infirmary, Aberdeen, UK.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Khan
authors.affiliation: Department of Radiology, Dumfries and Galloway Royal Infirmary, Dumfries, UK.
authors.forename: Petr
authors.initials: P
authors.lastname: Hrobar
authors.affiliation: Medical Unit, Dumfries and Galloway Royal Infirmary, Dumfries, UK.
authors.forename: Chris
authors.initials: C
authors.lastname: Isles
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D000072226:Computed Tomography Angiography / Q000706:statistics & numerical data*; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000378:metabolism*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011655:Pulmonary Embolism / Q000097:blood* / Q000000981:diagnostic imaging*; D012189:Retrospective Studies; D019564:Unnecessary Procedures
chemical_list: D015415:Biomarkers; D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D
keywords: Age-adjusted D-dimer; CTPA; D-dimer; Pulmonary embolism