title: Identifying transudates misclassified by Light's criteria.
abstract: OBJECTIVE
  Light's criteria combine three dichotomous tests into a decision rule that is considered positive if any one of the tests is positive. This strategy clearly maximizes sensitivity, although at the expense of specificity. Although Light's criteria identify 98% of pleural exudates, they misclassify about 25% of transudates as exudates. The way to overcome this limitation is discussed in this review.
  
  
  RESULTS
  Traditionally, measurement of the protein gradient between the serum and pleural fluid has been recommended to decrease the misclassification rate of Light's criteria. A recent study demonstrated that a gradient between the albumin levels in the serum and the pleural fluid more than 1.2 g/dl performs significantly better than a protein gradient more than 3.1 g/dl to correctly categorize mislabeled cardiac effusions (83 vs. 55%). On the other hand, the accuracy of a pleural fluid to serum albumin ratio less than 0.6 excelled when compared with albumin and protein gradients in patients with miscategorized hepatic hydrothoraces (77 vs. 62 vs. 61%).
  
  
  CONCLUSIONS
  The simplest strategy to reveal the true transudative nature of heart failure-related effusions, labeled as exudates by Light's criteria, is to calculate the serum to pleural fluid albumin gradient. Conversely, for misclassified hepatic hydrothoraces, measurement of the pleural to serum albumin ratio is recommended. The serum to pleural fluid protein gradient should no longer be considered the preferred test for this purpose.
authors.affiliation: Pleural Diseases Unit, Department of Internal Medicine, Arnau de Vilanova University Hospital, Biomedical Research Institute of Lleida, Lleida, Spain. jporcelp@yahoo.es
authors.forename: José M
authors.initials: JM
authors.lastname: Porcel
mesh_terms: D005122:Exudates and Transudates / Q000737:chemistry* / Q000378:metabolism; D005260:Female; D006333:Heart Failure / Q000378:metabolism; D006801:Humans; D006876:Hydrothorax / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008297:Male; D020097:Natriuretic Peptide, Brain / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism*; D010996:Pleural Effusion / Q000145:classification* / Q000378:metabolism; D015203:Reproducibility of Results; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism; D013194:Staining and Labeling
chemical_list: D010446:Peptide Fragments; D012709:Serum Albumin; C109794:pro-brain natriuretic peptide (1-76); D020097:Natriuretic Peptide, Brain; D007770:L-Lactate Dehydrogenase