title: Relationship between pleural fluid and serum cholesterol levels.
abstract: BACKGROUND
  Since the criteria of Light and colleagues for differentiating transudates and exudates were described, other tests, including the pleural fluid (PF) cholesterol test, have been proposed for the same purpose. However, the factors influencing PF cholesterol levels have not been clearly delineated.
  
  
  OBJECTIVE
  To analyze the relationships among total cholesterol (CHOL), low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol, and triglycerides (TRIG) in serum (S) and PF.
  
  
  METHODS
  PF and S from 99 patients (transudates, 13 patients; exudates, 86 patients) were analyzed for CHOL, HDL, LDL, TRIG, apolipoprotein AI, apolipoprotein B, and protein. The relationship between the PF and S level for each of these measurements was analyzed with linear regression and multiple regression using the ratio of PF to S protein for that measurement as a second independent variable.
  
  
  RESULTS
  This study demonstrated that CHOL levels in PF are related to S cholesterol levels and to the permeability of the pleura (r = 0.88; p < 0.001). However, the percentage of CHOL associated with LDL and HDL (56%) in the PF was much lower than that associated with LDL and HDL in S (93%), suggesting that lipoproteins are modified once they enter the pleural space. The PF TRIG was not closely related to its S level or to the PF/S protein ratio (r = 0.49).
  
  
  CONCLUSIONS
  PF cholesterol levels can be closely predicted from the S cholesterol levels and the permeability of the pleura, as reflected by the ratio of PF protein to S protein. Therefore, the CHOL ratio should not provide additional information to that provided by the protein ratio when trying to differentiate transudates from exudates. PF lipoproteins (LDL and HDL) undergo metabolic alterations once they enter the pleural space. PF TRIG levels are not closely related to S levels or to the permeability of the pleura.
authors.affiliation: Division of Respiratory Diseases, Heart Institute (InCor), University of São Paulo Medical School, São Paulo, Brazil.
authors.forename: M A
authors.initials: MA
authors.lastname: Vaz
authors.forename: L R
authors.initials: LR
authors.lastname: Teixeira
authors.forename: F S
authors.initials: FS
authors.lastname: Vargas
authors.forename: A O
authors.initials: AO
authors.lastname: Carmo
authors.forename: L
authors.initials: L
authors.lastname: Antonangelo
authors.forename: R
authors.initials: R
authors.lastname: Onishi
authors.forename: R W
authors.initials: RW
authors.lastname: Light
mesh_terms: D016632:Apolipoprotein A-I / Q000097:blood; D001055:Apolipoproteins B / Q000097:blood; D001798:Blood Proteins / Q000378:metabolism; D002784:Cholesterol / Q000097:blood*; D008076:Cholesterol, HDL / Q000097:blood; D008078:Cholesterol, LDL / Q000097:blood; D006801:Humans; D010996:Pleural Effusion / Q000175:diagnosis / Q000209:etiology / Q000378:metabolism*; D012016:Reference Values; D014280:Triglycerides / Q000097:blood
chemical_list: D016632:Apolipoprotein A-I; D001055:Apolipoproteins B; D001798:Blood Proteins; D008076:Cholesterol, HDL; D008078:Cholesterol, LDL; D014280:Triglycerides; D002784:Cholesterol