title: The use of pretest probability increases the value of high-resolution CT in diagnosing usual interstitial pneumonia.
abstract: BACKGROUND
  Recent studies have suggested that non-definitive patterns on high-resolution CT (HRCT) scan provide sufficient diagnostic specificity to forgo surgical lung biopsy in the diagnosis of idiopathic pulmonary fibrosis (IPF). The objective of this study was to determine test characteristics of non-definitive HRCT patterns for identifying histopathological usual interstitial pneumonia (UIP).
  
  
  METHODS
  Patients with biopsy-proven interstitial lung disease (ILD) and non-definitive HRCT scans were identified from two academic ILD centres. Test characteristics for HRCT patterns as predictors of UIP on surgical lung biopsy were derived and validated in independent cohorts.
  
  
  RESULTS
  In the derivation cohort, 64/385 (17%) had possible UIP pattern on HRCT; 321/385 (83%) had inconsistent with UIP pattern. 113/385 (29%) patients had histopathological UIP pattern in the derivation cohort. Possible UIP pattern had a specificity of 91.2% (95% CI 87.2% to 94.3%) and a positive predictive value (PPV) of 62.5% (95% CI 49.5% to 74.3%) for UIP pattern on surgical lung biopsy. The addition of age, sex and total traction bronchiectasis score improved the PPV. Inconsistent with UIP pattern demonstrated poor PPV (22.7%, 95% CI 18.3% to 27.7%). HRCT pattern specificity was nearly identical in the validation cohort (92.7%, 95% CI 82.4% to 98.0%). The substantially higher prevalence of UIP pattern in the validation cohort improved the PPV of HRCT patterns.
  
  
  CONCLUSIONS
  A possible UIP pattern on HRCT has high specificity for UIP on surgical lung biopsy, but PPV is highly dependent on underlying prevalence. Adding clinical and radiographic features to possible UIP pattern on HRCT may provide sufficient probability of histopathological UIP across prevalence ranges to change clinical decision-making.
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, California, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Brownell
authors.affiliation: Department of Medicine, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Teng
authors.initials: T
authors.lastname: Moua
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA.
authors.forename: Travis S
authors.initials: TS
authors.lastname: Henry
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA.
authors.forename: Brett M
authors.initials: BM
authors.lastname: Elicker
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Darin
authors.initials: D
authors.lastname: White
authors.affiliation: Department of Epidemiology and Biostatistics, University of California San Francisco, San Francisco, California, USA.
authors.forename: Eric
authors.initials: E
authors.lastname: Vittinghoff
authors.affiliation: Department of Pathology, University of California San Francisco, San Francisco, California, USA.
authors.forename: Kirk D
authors.initials: KD
authors.lastname: Jones
authors.affiliation: Department of Pathology, University of California San Francisco, San Francisco, California, USA.
authors.forename: Anatoly
authors.initials: A
authors.lastname: Urisman
authors.affiliation: Respiratory Diseases Department, Pontifical Catholic University, Santiago, Chile.
authors.forename: Carlos
authors.initials: C
authors.lastname: Aravena
authors.affiliation: Department of Medicine, University of Calgary, Calgary, Canada.
authors.forename: Kerri A
authors.initials: KA
authors.lastname: Johannson
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, California, USA.
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Golden
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, California, USA.
authors.forename: Talmadge E
authors.initials: TE
authors.lastname: King
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, California, USA.
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Wolters
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, California, USA.
authors.forename: Harold R
authors.initials: HR
authors.lastname: Collard
authors.affiliation: Department of Medicine, University of California San Francisco, San Francisco, California, USA.
authors.forename: Brett
authors.initials: B
authors.lastname: Ley
mesh_terms: D000368:Aged; D001706:Biopsy; D002140:California; D005260:Female; D006801:Humans; D017563:Lung Diseases, Interstitial / Q000000981:diagnostic imaging* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D008910:Minnesota; D011336:Probability; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000379:methods*
keywords: Histology/Cytology; Idiopathic pulmonary fibrosis; Interstitial Fibrosis; Thoracic Surgery