title: DLCO versus DLCO/VA as predictors of pulmonary gas exchange.
abstract: BACKGROUND
  The diffusing capacity of the lung is usually reported as both the diffusing capacity (DLCO) and the diffusing capacity divided by the alveolar volume (DLCO/VA). However, it is unclear which measure to use when interpreting pulmonary gas exchange. We therefore conducted this study to determine whether the DLCO or the DLCO/VA is a better predictor of oxygen desaturation with exercise.
  
  
  METHODS
  We retrospectively analyzed the pulmonary function records of all patients who had measurement of their diffusing capacity and 6-min walk oximetry in our university pulmonary function laboratory over a 2-year period.
  
  
  RESULTS
  There were data available on 97 patients, most of who had interstitial lung disease and/or lung volume restriction. The median DLCO was 51% predicted and the median DLCO/VA was 64% predicted. The prevalence of exercise desaturation was 43%. The overall sensitivity and specificity as determined by the area under the receiver operator characteristic (ROC) curve was higher for DLCO than DLCO/VA, with an optimal cut-off of normal of 55% predicted. The positive predictive values were equally low for both measures, ranging from 50% to 70%. After adjustment for VA, there were no differences between the ROC curves or predictive values for DLCO and DLCO/VA.
  
  
  CONCLUSIONS
  After adjusting for VA, neither the DLCO nor the DLCO/VA was better at predicting oxygen desaturation with exercise. The optimal cut-off of normal was 55% predicted.
authors.affiliation: Pulmonary Disease and Critical Care Medicine, University of Vermont College of Medicine, Given D-302, 89 Beaumont Avenue, Burlington, VT 05405, USA. david.kaminsky@uvm.edu
authors.forename: David A
authors.initials: DA
authors.lastname: Kaminsky
authors.forename: Todd
authors.initials: T
authors.lastname: Whitman
authors.forename: Peter W
authors.initials: PW
authors.lastname: Callas
mesh_terms: D000368:Aged; D004812:Epidemiologic Methods; D005080:Exercise Test; D005260:Female; D005541:Forced Expiratory Volume; D006801:Humans; D017563:Lung Diseases, Interstitial / Q000097:blood / Q000503:physiopathology*; D008176:Lung Volume Measurements; D008297:Male; D008875:Middle Aged; D010092:Oximetry; D010100:Oxygen / Q000097:blood; D011650:Pulmonary Alveoli / Q000473:pathology; D011653:Pulmonary Diffusing Capacity; D011659:Pulmonary Gas Exchange; D014797:Vital Capacity
chemical_list: D010100:Oxygen