title: Multilevel and continuous pleural fluid pH likelihood ratios for evaluating malignant pleural effusions.
abstract: OBJECTIVE
  Expert consensus recommends testing pleural fluid for pH to assist the selection of patients with malignant pleural effusions for pleurodesis. Although published studies report an association between pleural fluid pH and patient outcomes after pleurodesis, clinicians have no definitive information on how to use pH to select patients for pleurodesis. Thus, we quantitatively assessed different methods for deriving likelihood ratios from pleural fluid pH and evaluated the potential role of pH in selecting patients for pleurodesis.
  
  
  METHODS
  MEDLINE, systematic reviews, article reference lists, and contact with primary authors.
  
  
  METHODS
  Studies that assessed the impact of pleural fluid pH on survival and pleurodesis failure rates among patients with malignant pleural effusions.
  
  
  METHODS
  Primary authors provided their data in electronic spreadsheets.
  
  
  RESULTS
  Retrieved data sets included survival and pleurodesis failure rates for 417 patients and 433 patients, respectively. Binary, multilevel, and continuous likelihood ratios were calculated to estimate the likelihood of death within 3 months of pleurodesis or pleurodesis failure rates. Values for the likelihood ratios were compared for each of the three strategies, and relative clinical and statistical significance were assessed. Pleural fluid pH had marginal performance for identifying patients with < 3-month anticipated survival; binary likelihood ratios provided as much information as the multilevel and continuous strategies. Likelihood ratios for identifying patients likely to fail pleurodesis were clinically useful. Continuous likelihood ratios provided statistically more information as compared with the multilevel and binary strategies.
  
  
  CONCLUSIONS
  Pleural fluid pH has marginal value for estimating death within 3 months of pleurodesis, and binary likelihood ratios (cut point </= 7.20) perform as well as the other strategies assessed. Pleural fluid pH provides more useful information for estimating the likelihood of pleurodesis failure for which continuous likelihood ratios provide the most information as compared with binary or multilevel likelihood ratios.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Medical University of South Carolina, Charleston, SC 29425, USA. heffnerj@musc.edu
authors.forename: John E
authors.initials: JE
authors.lastname: Heffner
authors.forename: John N
authors.initials: JN
authors.lastname: Heffner
authors.forename: Lee K
authors.initials: LK
authors.lastname: Brown
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D006863:Hydrogen-Ion Concentration; D016013:Likelihood Functions; D018579:Patient Selection; D010996:Pleural Effusion / Q000737:chemistry*; D016066:Pleural Effusion, Malignant / Q000175:diagnosis* / Q000401:mortality; D018700:Pleurodesis; D017211:Treatment Failure