Introduction: 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.
Purpose: 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).
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.