title: [Influence of pleural fluid red blood cell count on the misidentification of transudates].
abstract: OBJECTIVE
  Light's criteria misclassify a quarter of transudates as exudates. We assessed the influence of red blood cell counts on pleural lactate dehydrogenase (LDH) levels and, thereby, on the specificity of Light's criteria.
  
  
  METHODS
  We retrospectively reviewed 1,312 consecutive patients with pleural effusion, of whom 1,014 were exudates and 298 transudates according to clinical criteria. The relationship between pleural erythrocytes and LDH using simple linear regression analysis, as well as the operating characteristics of Light's criteria, were assessed. Finally, a formula to correct pleural LDH levels, according to the erythrocyte count, was generated.
  
  
  RESULTS
  There was a linear relationship between the pleural erythrocyte count and LDH levels (r = 0.44; p < 0.001). Light's criteria yielded 81% specificity in patients with pleural erythrocyte counts < or = 10.000 3 10(6)/l, as compared to 61% in a group with a higher erythrocyte counts (p < 0.01). The application of the LDH formula enabled the correct reclassification of 24 of 64 (37%) false exudates.
  
  
  CONCLUSIONS
  A high pleural erythrocyte count, through its influence on the LDH levels, may lead to a transudate being misclassified as an exudate after applying Light's criteria.
authors.affiliation: Servicio de Medicina Interna. Hospital Universitario Arnau de Vilanova. Institut de Recerca Biomèdica de Lleida. Lleida. España. jporcelp@yahoo.es
authors.forename: José Manuel
authors.initials: JM
authors.lastname: Porcel
authors.forename: Aureli
authors.initials: A
authors.lastname: Esquerda
authors.forename: Montserrat
authors.initials: M
authors.lastname: Martínez
authors.forename: Francisco
authors.initials: F
authors.lastname: Rodríguez-Panadero
authors.forename: Silvia
authors.initials: S
authors.lastname: Bielsa
mesh_terms: D004906:Erythrocyte Count; D005122:Exudates and Transudates; D005260:Female; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D010996:Pleural Effusion / Q000737:chemistry / Q000166:cytology*; D012189:Retrospective Studies
chemical_list: D007770:L-Lactate Dehydrogenase