Pleural fluid tests to identify complicated parapneumonic effusions

Purpose of review Approximately 20% of patients with community-acquired pneumonia develop pleural effusions. In about 30% of these patients, the condition progresses to complicated parapneumonic effusion (CPPE) or to empyema. Pleural fluid analysis may aid decision-making for drainage in nonpurulent pleural fluids. Recent findings The classical pleural fluid criteria associated with a poor outcome without drainage are a pleural pH below 7.20, glucose below 60 mg/dl or a positive culture. Promising new biomarkers, in descending order of their likelihood ratios for detecting nonpurulent CPPE, include tumor necrosis factor-alpha, myeloperoxidase, matrix metalloproteinase-2, neutrophil elastase, interleukin-8, lipopolysaccharide-binding protein, terminal complement complex SC5b-9, soluble triggering receptor expressed on myeloid cell, matrix metalloproteinase-9, matrix metalloproteinase-8 and C-reactive protein. Pleural fluid procalcitonin lacks accuracy as a diagnostic marker of CPPE. Notably, the absence of an appropriate independent reference standard is a major limitation of all studies dealing with diagnostic tests for nonpurulent CPPE. Summary The proposed markers have similar operating characteristics as traditional pleural fluid biochemistries. However, their role in guiding therapeutic approach to parapneumonic effusions, particularly when classical parameters are not informative, warrants further study.