title: Accuracy of reduced-dose computed tomography for ureteral stones in emergency department patients.
abstract: OBJECTIVE
  Reduced-dose computed tomography (CT) scans have been recommended for diagnosis of kidney stone but are rarely used in the emergency department (ED) setting. Test characteristics are incompletely characterized, particularly in obese patients. Our primary outcome is to determine the sensitivity and specificity of a reduced-dose CT protocol for symptomatic ureteral stones, particularly those large enough to require intervention, using a protocol stratified by patient size.
  
  
  METHODS
  This was a prospective, blinded observational study of 201 patients at an academic medical center. Consenting subjects underwent both regular- and reduced-dose CT, stratified into a high and low body mass index (BMI) protocol based on effective abdominal diameter. Reduced-dose CT scans were interpreted by radiologists blinded to regular-dose interpretations. Follow-up for outcome and intervention was performed at 90 days.
  
  
  RESULTS
  CT scans with both regular and reduced doses were conducted for 201 patients, with 63% receiving the high BMI reduced-dose protocol. Ureteral stone was identified in 102 patients (50.7%) of those receiving regular-dose CT, with a ureteral stone greater than 5 mm identified in 26 subjects (12.9%). Sensitivity of the reduced-dose CT for any ureteral stone was 90.2% (95% confidence interval [CI] 82.3% to 95.0%), with a specificity of 99.0% (95% CI 93.7% to 100.0%). For stones greater than 5 mm, sensitivity was 100% (95% CI 85.0% to 100.0%). Reduced-dose CT identified 96% of patients who required intervention for ureteral stone within 90 days. Mean reduction in size-specific dose estimate was 18.6 milligray (mGy), from 21.7 mGy (SD 9.7) to 3.4 mGy (SD 0.9).
  
  
  CONCLUSIONS
  CT with substantial dose reduction was 90.2% (95% CI 82.3% to 95.0%) sensitive and 98.9% (95% CI 85.0% to 100.0%) specific for ureteral stones in ED patients with a wide range of BMIs. Reduced-dose CT was 96.0% (95% CI 80.5% to 99.3%) sensitive for ureteral stones requiring intervention within 90 days.
authors.affiliation: Department of Emergency Medicine, Yale University School of Medicine, New Haven, CT. Electronic address: Chris.Moore@yale.edu.
authors.forename: Christopher L
authors.initials: CL
authors.lastname: Moore
authors.affiliation: Department of Emergency Medicine, Yale University School of Medicine, New Haven, CT.
authors.forename: Brock
authors.initials: B
authors.lastname: Daniels
authors.affiliation: Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT.
authors.forename: Monica
authors.initials: M
authors.lastname: Ghita
authors.affiliation: Department of Diagnostic Radiology, Yale University School of Medicine, New Haven, CT.
authors.forename: Gowthaman
authors.initials: G
authors.lastname: Gunabushanam
authors.affiliation: Department of Emergency Medicine, Yale University School of Medicine, New Haven, CT.
authors.forename: Seth
authors.initials: S
authors.lastname: Luty
authors.affiliation: Departments of Neurosurgery and Epidemiology and Biostatistics, University of San Francisco School of Medicine, San Francisco, CA.
authors.forename: Annette M
authors.initials: AM
authors.lastname: Molinaro
authors.affiliation: Department of Urology, Yale University School of Medicine, New Haven, CT.
authors.forename: Dinesh
authors.initials: D
authors.lastname: Singh
authors.affiliation: Department of Internal Medicine, Yale University School of Medicine, New Haven, CT.
authors.forename: Cary P
authors.initials: CP
authors.lastname: Gross
mesh_terms: D000046:Academic Medical Centers; D000328:Adult; D015992:Body Mass Index; D004636:Emergency Service, Hospital; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011829:Radiation Dosage; D014057:Tomography, X-Ray Computed / Q000379:methods; D014513:Ureter / Q000000981:diagnostic imaging*; D014514:Ureteral Calculi / Q000000981:diagnostic imaging*