Finally, a bivariate correlation analysis (Pearson) was used to test for significant linear relationship between polymorphonuclear leukocyte counts and levels of TNF-a in pleural fluid. A two-tailed p value < 0.05 was considered significant. Data were analyzed by using the SPSS statistical package (version 10.0; SPSS; Chicago, IL). с
The study population comprised 80 patients (60 men and 20 women), with a median age of 62 years (quartiles, 42 to 75) years. Of these, 35 patients had UPPE, 23 patients had CPPE, and 22 patients had empyema. Overall, pleural fluid culture findings were positive in 23 of 74 patients (31%), aerobic Gram-positive bacteria being isolated in 13 cases. Categorization of PPE among the patients with culture-positive fluids was as follows: UPPE (n = 2), CPPE (n = 7), and empyema (n = 14).
Table 1 shows clinical and pleural fluid characteristics for the three different types of PPE. As expected, patients with CPPE presented more frequently with large effusions and positive culture findings, and their pleural fluids had lower pH and glucose contents, and higher LDH concentrations than those observed in patients with UPPE. Empyema fluids exhibited particularly high values of leukocytes, ADA, and pleural fluid-to-serum (P/S) LDH ratios when compared to the remainder groups.
Median TNF-a levels in pleural fluid were significantly higher in CPPE (133.0 pg/mL) and empyema (142.2 ng/mL) than in UPPE (39.1 ng/mL, p < 0.001), but no statistical difference was found between the first two groups (Fig 1).
Table 1—Characteristics of the Study Population

Figure 1. Distribution of pleural TNF-a in the three different classes of parapneumonic effusions.
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