OPA16 OPTIMISING PLEURAL FLUID ADA AND ASSOCIATED BIOMARKERS FOR DIAGNOSING TUBERCULOUS PLEURAL EFFUSION: A LOCAL VALIDATION STUDY

Afifah Kamarudin¹, Woo Fui Bee¹, Shoban Raj A/L Manoraj¹, Liew Min¹, Janaardhan A/L Thikaran¹, Anez Aslan¹, Raymund Dass¹, Han Loong Tan¹
¹Respiratory Unit, Department of Internal Medicine, Hospital Tuanku Ja’afar Seremban, Malaysia

Introduction
Pleural fluid adenosine deaminase (ADA) is a useful biomarker for diagnosing tuberculous pleural effusion (TPE), though optimal cutoff values vary. This study evaluates the best ADA threshold for local use.

Objectives
To identify the optimal pleural ADA cutoff for diagnosing TPE and explore disease characteristics linked to elevated ADA levels.

Methodology
A retrospective study reviewed pleural fluid ADA samples collected from 2022 to 2023. Receiver Operating Characteristic (ROC) curve analysis was performed to identify the optimal ADA cutoff for diagnosing TPE, with the Area Under the Curve (AUC) used to evaluate test performance.

Results
92 patients were included (mean age 55.9 years, 63% male). Most effusions (88.0%) were exudative; 22.8% were malignant and 77.2% non-malignant. Among the non-malignant effusions, 46.5% were due to pleural infection, 31.0% TPE and 14.1% transudative effusion. Mean ADA levels were 16.5 U/L in malignant effusions, 68.9 U/L in TPE, and 89.3 U/L in pleural infections (p < 0.001 for all groups). An ADA threshold of 37.75 U/L was identified as optimal for diagnosing TPE. The highest mean pleural LDH 1051.7 U/L was found in TPE, followed by a parapneumonic effusion and malignant effusion at 878.5 U/L and 809 U/L respectively

Conclusion
A pleural fluid ADA cutoff of 37.75 U/L demonstrated strong diagnostic accuracy for TPE. This finding, coupled with other biochemical parameters, support its use as a reliable, non-invasive marker to distinguish TPE from other exudative effusions.