OBJECTIVES: Delay in the treatment of pleural infection may contribute to its high mortality. In this retrospective study, we aimed to evaluate the diagnostic accuracy of pleural adenosine deaminase in discrimination between Gram-negative and Gram-positive bacterial infections of the pleural space prior to selecting antibiotics. METHODS: A total of 76 patients were enrolled and grouped into subgroups according to Gram staining: 1) patients with Gram-negative bacterial infections, aged 53.2±18.6 years old, of whom 44.7% had empyemas and 2) patients with Gram-positive bacterial infections, aged 53.5±21.5 years old, of whom 63.1% had empyemas. The pleural effusion was sampled by thoracocentesis and then sent for adenosine deaminase testing, biochemical testing and microbiological culture. The Mann-Whitney U test was used to examine the differences in adenosine deaminase levels between the groups. Correlations between adenosine deaminase and specified variables were also quantified using Spearman’s correlation coefficient. Moreover, receiver operator characteristic analysis was performed to evaluate the diagnostic accuracy of pleural effusion adenosine deaminase. RESULTS: Mean pleural adenosine deaminase levels differed significantly between Gram-negative and Gram-positive bacterial infections of the pleural space (191.8±32.1 U/L vs 81.0±16.9 U/L, p<0.01). The area under the receiver operator characteristic curve was 0.689 (95% confidence interval: 0.570, 0.792, p<0.01) at the cutoff value of 86 U/L. Additionally, pleural adenosine deaminase had a sensitivity of 63.2% (46.0-78.2%); a specificity of 73.7% (56.9-86.6%); positive and negative likelihood ratios of 2.18 and 0.50, respectively; and positive and negative predictive values of 70.6% and 66.7%, respectively. CONCLUSIONS: Pleural effusion adenosine deaminase is a helpful alternative biomarker for early and quick discrimination of Gram-negative from Gram-positive bacterial infections of the pleural space, which is useful for the selection of antibiotics.

OBJECTIVES: Our previous study demonstrated that superoxide dismutase levels were higher in tuberculous pleural effusions than in malignant pleural effusions, but that this difference could not be used to discriminate between the two. The objective of the present study was to investigate the levels of superoxide dismutase 2 in pleural effusions and to evaluate the diagnostic significance of pleural effusion superoxide dismutase 2. METHODS: Superoxide dismutase 2 concentrations were determined in pleural effusions from 54 patients with tuberculous pleural effusion and 33 with malignant pleural effusion using an enzyme-linked immunosorbent assay (ELISA) kit. Pleural effusion interferon gamma and tumor necrosis factor alpha levels were also analyzed by ELISA. The Mann-Whitney U test was used to evaluate the significance of differences. Associations between superoxide dismutase 2 concentrations and sex, age and smoking habits were assessed using Spearman's or Pearson's correlation coefficient analysis. Receiver operator characteristic analysis was performed to evaluate the value of superoxide dismutase 2 levels in the discrimination of tuberculous pleural effusion from malignant pleural effusion. RESULTS: Superoxide dismutase 2 levels were significantly higher in patients with tuberculous pleural effusion compared with those with malignant pleural effusion (p<0.05). When superoxide dismutase 2 was used to differentiate between tuberculous pleural effusions and malignant pleural effusions, the area under the receiver operator characteristic curve was 0.909 (95% confidence interval, 0.827-0.960; p<0.01). With a cut-off value of 54.2 ng/mL, the sensitivity, specificity, positive likelihood ratio and negative likelihood ratio were 75.8% (95%CI: 57.7-88.9%), 98.1% (95%CI: 90.1-99.7%), 40.91 and 0.25, respectively. Furthermore, significant correlations between pleural effusion superoxide dismutase 2 and interferon gamma (r = 0.579, p<0.01) and between pleural effusion superoxide dismutase 2 and tumor necrosis factor alpha (r = 0.396, p<0.01) were observed. CONCLUSION: Pleural effusion superoxide dismutase 2 can serve as a biomarker for differentiating between tuberculous pleural effusions and malignant pleural effusions. Because of the high correlations of superoxide dismutase 2 with pleural effusion interferon gamma and tumor necrosis factor alpha levels, this marker may act as an inflammatory factor that plays an important role in the development of tuberculous pleural effusion.