Purpose: Diuretic therapy increases the total protein and lactate dehydrogenase concentrations in pleural fluid in patients with transudates due to heart failure, but the effect of diuresis on other substances in pleural fluid constituents is not known.
Subjects and methods: Twenty-one patients with transudative pleural effusions due to congestive heart failure were prospectively studied. Repeated diagnostic thoracentesis (mean +/- SD = 3 +/- 1; range, 2 to 6) was performed until the effusions were radiographically unapparent (5 +/- 2 days). Thirty-one patients with congestive heart failure who underwent only a single thoracentesis after diuretic therapy served as controls. We measured the concentrations of various components of pleural effusions in the serum and in the pleural fluid, and determined the serum-pleural fluid gradient (serum concentration minus pleural fluid concentration) and ratio (serum concentration divided by pleural fluid concentration).
Results: The pleural concentrations of most components increased significantly (P <0.001) from the initial specimen to the final specimen: total protein, from 23 +/- 7 g/L to 33 +/- 9 g/L; albumin, from 13 +/- 4 g/L to 18 +/- 6 g/L; lactate dehydrogenase, from 177 +/- 62 U/L to 288 +/- 90 U/L; cholesterol, from 31 +/- 16 mg/dL to 52 +/- 22 mg/dL; and cholinesterase, from 1,304 +/- 616 U/L to 1,884 +/- 674 U/L. Expressed as percentage change, the increases in the serum-pleural fluid gradients for albumin (12% +/- 22%) and total protein (11% +/- 12%) were significantly less than the increases in their concentrations in pleural fluid (albumin, 47% +/- 49%; total protein, 48% +/- 40%) or in their pleural fluid/serum ratios (albumin, 27% +/- 29%; total protein, 38% +/- 34%).
Conclusions: The concentrations of the biochemical components commonly measured in pleural fluid increase progressively during diuretic therapy. Calculation of the serum-pleural fluid gradients for protein and albumin may be the most useful way to distinguish transudates from exudates in patients with congestive heart failure who have undergone diuresis.