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Multilevel Likelihood Ratios for Identifying Exudative Pleural Effusions*
Study objectives: To determine multilevel likelihood ratios for pleural fluid tests that are commonly used to discriminate between exudative and transudative pleural effusions.
Design: Meta-analysis of patient-level data.
Patient data: Selected studies included patients with diagnoses of exudative or transudative pleural effusions who underwent thoracentesis and laboratory analysis of their pleural fluid.
Measurements and methods: Studies were identified by searching MEDLINE and related bibliographies. Data were obtained for 1,448 patients from seven primary investigators or extracted from dot plots in published reports. Likelihood ratios were calculated from extracted data stratified across ranges of test result values.
Results: Sufficient data were available to calculate multilevel likelihood ratios for the elements of Light's criteria (pleural fluid lactate dehydrogenase [LDH], ratio of pleural fluid to serum LDH, and ratio of pleural fluid to serum protein), pleural fluid protein, ratio of pleural fluid to serum cholesterol, pleural fluid cholesterol, and gradient of pleural fluid to serum albumin. Each of these tests provided levels of likelihood ratios through the most clinically relevant range (0 to 10).
Conclusion: Multilevel likelihood ratios combined with a clinician's estimation of the pretest probability of an exudative effusion improve the diagnostic accuracy of discriminating between exudative and transudative pleural effusions. Likelihood ratios avoid the use of confusing terms, such as "pseudoexudates," that derive from the use of single cutoff points for pleural fluid tests.
(CHEST 2002; 121:1916-1920)
Key words: body fluids; pleura; pleural disease; pleural effusion; thoracentesis
Abbreviations: LDH = lactate dehydrogenase; LDH-PF = pleural fluid lactate dehydrogenase expressed as a fraction of the upper limits of normal for the serum assay; LDH-R = ratio of pleural fluid to serum lactate dehydrogenase
Pleural effusions of uncertain etiology are extremely common diagnostic challenges that warrant thoracentesis and pleural fluid analysis to categorize the effusion as an exudate or transudate. Because exudative effusions present a broad differential diagnosis of various inflammatory and malignant conditions that often require additional diagnostic or therapeutic interventions,1 accurate categorization of an effusion is fundamentally important.
Multiple investigations have examined the discriminative properties of different pleural fluid tests for identifying exudative effusions.2-10 These studies usually compare the operating characteristics of individual tests among patients with different etiologies of pleural effusions in order...