title: Validation of the lower limit of normal diffusing capacity for detecting emphysema.
abstract: BACKGROUND
  Diffusing capacity for carbon monoxide (D(Lco)) has been regarded as reliable for detecting emphysema. The lower 5th percentile of the reference population has been used as the lower limit of normal (LLN) for D(Lco), without clinical validation.
  
  
  OBJECTIVE
  We performed this study to validate the LLN for D(Lco) and to determine the optimum cutoff LLN value for detecting emphysema.
  
  
  METHODS
  A total of 197 COPD patients and 103 healthy adult subjects were included. COPD patients with emphysema were defined as COPD patients in whom volumetric CT showed that the volume fraction of the lung at less than -950 Hounsfield units at full inspiration was more than 15%. All other COPD patients were defined as COPD patients without emphysema. All measured D(Lco) values were transformed to estimates of reference population percentiles. ROC curve analysis was used to validate and to determine the optimum cutoff percentile value as the LLN for D(Lco).
  
  
  RESULTS
  Of the 197 COPD patients, 126 were classified as having emphysema and 71 as without emphysema. On ROC curve analysis, the lower 5th percentile used as the LLN for D(Lco) had a sensitivity of 68.3% and a specificity of 98.1% to differentiate COPD patients with emphysema from healthy subjects. The lower 9th percentile was the best LLN cutoff value for detecting COPD patients with emphysema.
  
  
  CONCLUSIONS
  The lower 5th percentile of the reference population may not be the best LLN cutoff value for D(Lco) for detecting emphysema.
authors.affiliation: Department of Pulmonary and Critical Care Medicine and Clinical Research Center for Chronic Obstructive Airway Diseases, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Republic of Korea.
authors.forename: Jae Seung
authors.initials: JS
authors.lastname: Lee
authors.forename: Seung Won
authors.initials: SW
authors.lastname: Ra
authors.forename: Eun Jin
authors.initials: EJ
authors.lastname: Chae
authors.forename: Joon Beom
authors.initials: JB
authors.lastname: Seo
authors.forename: Seong Yong
authors.initials: SY
authors.lastname: Lim
authors.forename: Tae-Hyung
authors.initials: TH
authors.lastname: Kim
authors.forename: Sang-Do
authors.initials: SD
authors.lastname: Lee
authors.forename: Yeon-Mok
authors.initials: YM
authors.lastname: Oh
mesh_terms: D000368:Aged; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011653:Pulmonary Diffusing Capacity; D029424:Pulmonary Disease, Chronic Obstructive / Q000150:complications; D011656:Pulmonary Emphysema / Q000150:complications / Q000175:diagnosis* / Q000000981:diagnostic imaging; D011859:Radiography; D012680:Sensitivity and Specificity; D014797:Vital Capacity