Quantitative analysis of pleural fluid cell-free DNA as a tool for the classification of pleural effusions.
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.
Chan
Michael H M
MH
Department of Chemical Pathology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR.
Chow
Kai Ming
KM
Chan
Anthony T C
AT
Leung
Chi Bon
CB
Chan
Lisa Y S
LY
Chow
Katherine C K
KC
Lam
Ching Wan
CW
Lo
Y M Dennis
YM
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
D005914:Globins; D004247:DNA