Biochemical Markers in Pleural Fluid for the Diagnosis of Tuberculous Pleural Effusion: A Retrospective Study.

BACKGROUND/

OBJECTIVES

The rapid diagnosis of tuberculous pleural effusion (TPE) presents significant challenges for clinicians due to its paucibacillary nature. Routine biochemical markers may complement microbiological and molecular tests, especially in resource-limited settings. The objective of this study was to evaluate the diagnostic performance of pleural fluid adenosine deaminase (ADA), lactate dehydrogenase (LDH), total protein (TP), and the ADA/LDH and ADA/TP ratios for tuberculous pleural effusion, using Löwenstein-Jensen culture and Xpert MTB/RIF as microbiological reference standards

Methods

We conducted a retrospective study (2016-2024) including 325 consecutive patients investigated for suspected TPE in a tertiary hospital. ADA, TP and LDH were measured, and additional ratio-based indices (ADA/TP, ADA/LDH) were calculated for 325 pleural fluid (PF) samples. Löwenstein-Jensen (LJ) culture (with MPT64 confirmation) and GeneXpert MTB/RIF (Xpert MTB/RIF) were used as separate microbiological reference standards. Sensitivity (Se), specificity (Sp), and areas under the ROC curve (AUC) were estimated, and optimal thresholds were determined using the Youden index.

RESULTS

Among 325 pleural fluid samples, 23 (7.1%) were culture-positive. Xpert MTB/RIF was performed in 73/325 patients (22.5%), with Mycobacterium tuberculosis detected in 19/73 (26.0%) tested samples. In PF, ADA provided the best performance against culture, with Se of 100%. Correlation analysis in PF showed a moderate positive association between TP and LDH (p < 0.0001).

CONCLUSIONS

Among routine biochemical markers, PF ADA shows high NPV. Integrating these rapid, low-cost tests alongside LJ culture and Xpert MTB/RIF may streamline the diagnostic pathway for TPE.