Thus, detection of gross pus means that patient has an empyema, which is an absolute indication for drainage. Pleural drainage will also most likely be needed for patients with positive pleural fluid culture findings, yet up to 90%, 70%, and 25% of UPPEs, CPPEs, and empyemas, respectively, have negative bacteriologic fluid examination findings. In addition, it is our experience that approximately 10% of patients with positive pleural culture findings respond to antibiotics alone.
In clinical practice, the biochemical characteristics of pleural fluid are the cornerstone to discriminate which patients have CPPE. A guideline for the treatment of PPE published by the American College of Chest Physicians stated that the presence of a low pleural fluid pH (< 7.20) or glucose (< 60 mg/dL) are usually associated with a poor prognosis, thus needing more aggressive therapeutic maneuvers. Light also included pleural fluid LDH in his classification scheme for PPE in that levels > 1,000 U/L define a borderline CPPE. A meta-analysis of these three biochemical indexes revealed that pleural fluid pH was a little better for identifying non-purulent CPPE (AUC = 0.89) than was the pleural fluid glucose or LDH (AUC = 0.71), although multiple design problems in the primary studies caution the interpretation of data. We found considerable overlap between the AUC values for pH (AUC = 0.78), glucose (AUC = 0.82), and LDH (AUC = 0.86), but there was a trend toward a better accuracy of the latter, mainly due to its superior sensitivity.
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