Pleural Fluid pH and Lactate Dehydrogenase as Predictors of Tube Thoracostomy in Parapneumonic Effusion

This study was conducted to determine the prognostic value of pleural fluid pH and lactate dehydrogenase (LDH) to predict the occurrence of tube thoracostomy in patients with parapneumonic effusion. This study was Prospective observational cohort, conducted at Saidu Teaching Hospital Swat, from August 2024 to July 2025. Pleural fluid was analyzed for pH and lactate dehydrogenase (LDH) levels. The primary outcome was the requirement for tube thoracostomy, decided by the treating clinical team based on standard guidelines. Receiver operating characteristic (ROC) curve analysis was used to determine optimal biomarker cut-off values for predicting drainage. Secondary outcomes were time to defervescence, hospital length of stay, treatment failure necessitating VATS and in-hospital mortality. Multivariate logistic regression was employed to identify independent predictors. The analysis of pleural fluids showed a deterioration of pH level and an increase in LDH in CPPE patients as compared to uncomplicated cases (pH: 7.08 vs. 7.38; LDH: 2840 vs. 756 IU/L; p < 0.001). The receiver operating characteristic (ROC) analysis was used to determine the best cut-off value of pH 7.18 or less (AUC: 0.92, sensitivity 88% specificity 86%) and LDH 1120 or more IU/L (AUC: 0.88, sensitivity 85% specificity 82%). There was no significant improvement in discrimination from the combined model (AUC 0.93) compared to pH alone (DeLong's test p = 0.42); the combined model had a specificity of 95%. Biomarkers were confirmed as independent predictors of drainage requirement (pH: OR 12.4; LDH: OR 8.1) by multivariate analysis. The results of this study confirm that pleural fluid pH and LDH are valuable and convenient biomarkers to inform drainage in parapneumonic effusions to promote better clinical outcomes and resource use.