title: Determination of total proteins and lactate dehydrogenase for the diagnosis of pleural transudates and exudates: redefining the classical criterion with a new statistical approach.
abstract: OBJECTIVE
  To propose a new classification criterion for the differentiation between pleural exudates and transudates-quantifying total proteins in pleural fluid (TP-PF) and lactate dehydrogenase in pleural fluid (LDH-PF) exclusively-as well as to compare this new criterion with the classical criterion in terms of diagnostic yield.
  
  
  METHODS
  This was an observational, cross-sectional study with a within-subject design, comprising 181 patients with pleural effusion treated at two university hospitals in the state of Rio de Janeiro, Brazil, between 2003 and 2006. The diagnostic parameters included in the classical criterion were identified, as were those included in the new criterion.
  
  
  RESULTS
  Of the 181 patients, 152 and 29 were diagnosed with pleural exudates and pleural transudates, respectively. For the classical criterion, the sensitivity, specificity, and accuracy for the diagnosis of pleural exudates were, respectively, 99.8%, 68.6%, and 94.5%, whereas the corresponding values for the diagnosis of pleural transudates were 76.1%, 90.1%, and 87.6%. For the new criterion (cut-off points set at 3.4 g/dL for TP-PF and 328.0 U/L for LDH-PF), the sensitivity, specificity, and accuracy for the diagnosis of exudates were, respectively, 99.4%, 72.6%, and 99.2%, whereas the corresponding values for the diagnosis of transudates were 98.5%, 83.4%, and 90.0%. The accuracy of the new criterion for the diagnosis of pleural exudates was significantly greater than was that of the classical criterion (p = 0.0022).
  
  
  CONCLUSIONS
  The diagnostic yield was comparable between the two criteria studied. Therefore, the new classification criterion can be used in daily practice.
authors.affiliation: Faculdade de Medicina, Universidade Federal do Estado do Rio de Janeiro, Rio de Janeiro, Brasil. b.c.maranhao@uol.com.br
authors.forename: Bernardo Henrique Ferraz
authors.initials: BH
authors.lastname: Maranhão
authors.forename: Cyro Teixeira da
authors.initials: CT
authors.lastname: Silva Junior
authors.forename: Antonio Monteiro da Silva
authors.initials: AM
authors.lastname: Chibante
authors.forename: Gilberto Perez
authors.initials: GP
authors.lastname: Cardoso
mesh_terms: D000293:Adolescent; D000328:Adult; D002648:Child; D003948:Diagnostic Techniques, Respiratory System / Q000592:standards*; D004812:Epidemiologic Methods; D005122:Exudates and Transudates; D005260:Female; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000032:analysis*; D008297:Male; D010996:Pleural Effusion / Q000175:diagnosis*; D011506:Proteins / Q000032:analysis*; D012016:Reference Values; D055815:Young Adult
chemical_list: D011506:Proteins; D007770:L-Lactate Dehydrogenase