What is the key question?

• Are neutrophil extracellular traps (NETs) concentrations higher in parapneumonic effusions compared with effusions of other origin and does this reflect the inflammatory nature of these effusions?

What is the bottom line?

• A total of 101 patients seeking hospital treatment for undifferentiated pleural effusion underwent pleural fluid classification based on cytologic analysis results, biochemical findings, microbiological characteristics, and clinical judgement. Concentrations of NET markers (extracellular DNA [eDNA], citrullinated histone H3 [citH3]), neutrophils (α-defensins), and inflammation (IL-1β)-related proteins were quantified by enzyme-linked immunosorbent assay.
• Effusions were classified into four groups: parapneumonic (n=18), malignant (n=35), transudative (n=22), and unclassifiable (n=26). Concentrations of NETs markers were significantly higher in the parapneumonic group compared with malignant, transudative, and unclassifiable groups (P < 0.001).
• citH3 and eDNA correlated highly with lactate dehydrogenase (P < 0.001) and had moderate negative correlation with pH (P < 0.001). α-Defensins and IL-1β were higher in the parapneumonic group than in other groups (P < 0.001) and correlated moderately with lactate dehydrogenase (P < 0.001). ROC curves showed high sensitivity and specificity for NET markers for prediction of parapneumonic effusion.

Why read on?

• We learn from this study that high levels of some NET-related mediators in parapneumonic effusions correlate with inflammation unlike pleural effusions of other causes. Since NETs may be an important contributor to the inflammation and viscosity of parapneumonic effusions, the findings from this study may shed the light on the therapeutic benefit of deoxyribonuclease in empyema.