title: Computed Tomography Angiography in Patients Evaluated for Acute Pulmonary Embolism with Low Serum D-dimer Levels: A Prospective Study.
abstract: BACKGROUND
  Pulmonary computed tomography angiography (CTA) and the Wells criteria both have interobserver variability in the assessment of pulmonary embolism (PE). Quantitative D-dimer assay findings have been shown to have a high negative predictive value in patients with low pretest probability of PE.
  
  
  OBJECTIVE
  Evaluate roles for clinical probability and CTA in Emergency Department (ED) patients suspected of acute PE but having a low serum D-dimer level.
  
  
  METHODS
  Prospective observational study of ED patients with possible PE who underwent pulmonary CTA and had D-dimer levels </=1.0 mug/mL.
  
  
  RESULTS
  Clinical probability of PE determined by ED physicians using standard published criteria; pulmonary CTAs read by initial and study radiologists kept unaware of D-dimer results.
  
  
  RESULTS
  In 16 months, 744 patients underwent pulmonary CTA, with 347 study participants who had a D-dimer level </= 1.0 mug/mL. In one participant, CTA showed a PE that was agreed on by both the initial and study radiologists. In six participants, the initial findings were reported as positive for PE but were not interpreted as positive by the study radiologist. In none of these participants was PE diagnosed on the basis of clinical probability, of findings on ancillary studies and three-month follow-up examination, or by another radiologist, unaware of findings, acting as a tiebreaker.
  
  
  CONCLUSIONS
  Pulmonary CTA findings positive for acute embolism should be viewed with caution, especially if the suspected PE is in a distal segmental or subsegmental artery in a patient with a serum D-dimer level of </=1.0 mug/mL. Furthermore, the Wells criteria may be of limited additional value in this group of patients with low D-dimer levels because most will have low or intermediate clinical probability of PE.
authors.affiliation: Lana Hirai Gimber, MPH, is a fourth-year medical student at the John A Burns School of Medicine in Honolulu, HI. E-mail: lanakhirai@yahoo.com .
authors.forename: Lana Hirai
authors.initials: LH
authors.lastname: Gimber
authors.forename: R Ing
authors.initials: RI
authors.lastname: Travis
authors.forename: Jayme M
authors.initials: JM
authors.lastname: Takahashi
authors.forename: Torrey L
authors.initials: TL
authors.lastname: Goodman
authors.forename: Hyo-Chun
authors.initials: HC
authors.lastname: Yoon