title: Quantitative analysis of pleural fluid cell-free DNA as a tool for the classification of pleural effusions.
abstract: BACKGROUND
  Recently, much interest has been focused on the quantification of DNA in miscellaneous body fluids. In this study, the application is extended to classifying pleural effusions by measuring cell-free DNA in pleural fluid.
  
  
  METHODS
  We recruited 50 consecutive patients with pleural effusions with informed consent. Pleural fluids were centrifuged at 13000 g, with supernatants aliquoted for extraction and analysis of beta-globin DNA sequence by quantitative real-time PCR. Serum and pleural fluid biochemistries were performed to classify pleural effusions using the modified criteria of Light et al. (Ann Intern Med 1972;77:507-13). The ROC curve was plotted to determine the cutoff DNA concentration for classifying pleural fluids as transudates or exudates. Indicators of diagnostic accuracy were calculated for both pleural fluid DNA and modified criteria of Light et al., using the discharge, microbiologic, and histologic diagnoses as the reference standard.
  
  
  RESULTS
  The area under the ROC curve was 0.95 [95% confidence interval (CI), 0.84-0.99]. At 509 genome-equivalents/mL, pleural fluid DNA alone correctly classified 46 of 50 pleural effusions with 91% sensitivity (95% CI, 76-98%), 88% specificity (95% CI, 64-98%), and positive and negative likelihood ratios of 7.7 (95% CI, 3.1-19.5) and 0.10 (95% CI, 0.04-0.27), respectively. With the modified criteria of Light et al., 43 of 50 pleural effusions were correctly classified with 97% sensitivity (95% CI, 91-100%) and 67% specificity (95% CI, 45-89%). There were significant correlations between cell-free DNA and both lactate dehydrogenase and total protein in pleural fluid, suggesting their common origin.
  
  
  CONCLUSIONS
  Pleural fluid DNA concentrations are markedly increased in exudative effusions, making it a potential new tool to evaluate the etiologic causes of pleural effusions.
authors.affiliation: Department of Chemical Pathology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR.
authors.forename: Michael H M
authors.initials: MH
authors.lastname: Chan
authors.forename: Kai Ming
authors.initials: KM
authors.lastname: Chow
authors.forename: Anthony T C
authors.initials: AT
authors.lastname: Chan
authors.forename: Chi Bon
authors.initials: CB
authors.lastname: Leung
authors.forename: Lisa Y S
authors.initials: LY
authors.lastname: Chan
authors.forename: Katherine C K
authors.initials: KC
authors.lastname: Chow
authors.forename: Ching Wan
authors.initials: CW
authors.lastname: Lam
authors.forename: Y M Dennis
authors.initials: YM
authors.lastname: Lo
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002648:Child; D004247:DNA / Q000032:analysis*; D005122:Exudates and Transudates / Q000737:chemistry* / Q000166:cytology; D005260:Female; D005914:Globins / Q000032:analysis / Q000235:genetics; D006801:Humans; D008297:Male; D008875:Middle Aged; D010996:Pleural Effusion / Q000145:classification* / Q000175:diagnosis / Q000209:etiology; D016133:Polymerase Chain Reaction; D011446:Prospective Studies; D012372:ROC Curve
chemical_list: D005914:Globins; D004247:DNA