Beyond light's criteria: pleural lactate predicts need for tube thoracostomy in complicated parapneumonic effusions

Differentiation of pleural effusions and identification of complicated parapneumonic effusions remain important challenges in clinical practice. Although Light's criteria are routinely applied, additional pleural fluid parameters may provide complementary information in selected patients.

To evaluate the diagnostic performance of pleural fluid lactate and the pleural fluid-to-blood lactate ratio in pleural effusions and to examine their association with complicated parapneumonic effusions and drainage approach.

This study included 110 patients who underwent pleural drainage. Paired pleural fluid and venous blood samples were obtained prior to drainage, and lactate levels were measured using a blood gas analyser. Pleural effusions were classified according to Light's criteria. Diagnostic performance was assessed using receiver operating characteristic analysis.

Of the 110 patients, 90 (81.8%) had exudative and 20 (18.2%) transudative effusions. Pleural fluid lactate and the pleural fluid-to-blood lactate ratio showed good discrimination between exudative and transudative effusions (AUC 0.912 and 0.883, p < 0.001), while blood lactate alone had limited diagnostic value. No significant correlation was observed between pleural and blood lactate levels. In patients with complicated parapneumonic effusions, higher pleural fluid lactate levels were associated with complicated effusions (cut-off 5.45 mmol/L; AUC 0.883). Elevated pleural fluid lactate values were also more frequently observed in patients who required tube thoracostomy (cut-off 4.05 mmol/L; AUC 0.920).

Pleural fluid lactate may serve as a useful adjunct to standard pleural fluid analysis. Its measurement could assist in the assessment of disease severity and drainage requirements in parapneumonic effusions; however, further prospective studies are warranted.