Diagnostic performance and optimal cut-off values of pleural fluid adenosine deaminase in diagnosing TB pleural effusion among adult patients at the Lung Center of the Philippines: a cross-sectional analytical study

Abstract

Background:

Tuberculosis (TB) remains a major global health threat, with 10.6 million cases and 1.3 million deaths in 2023. In the Philippines, 591,000 cases and 31,000 deaths were reported. Tuberculous pleural effusion (TPE) is difficult to diagnose due to low test sensitivity. Pleural fluid adenosine deaminase (pfADA) offers a simple, cost-effective marker, though optimal cut-offs vary. This study assesses pfADA’s diagnostic accuracy in Filipino adults and determines appropriate local cut-off values for TPE.

Objectives:

The general objective is to appraise pfADA's diagnostic effectiveness in TB pleural effusion compared to other standard references. Specific goals include determining pfADA's accuracy, sensitivity, specificity, positive and negative predictive values, and discriminative ability through ROC curves. Subgroup analyses seek optimal cut-off points for differentiating TB from non-TB effusions in patients with TB, age >45, and a history of TB treatment at least two years prior.

Methods:

This retrospective, analytical, cross-sectional study involves adults with exudative, lymphocytic-predominant pleural effusion at the Lung Center of the Philippines (April–November 2023). Data encompass demographics, clinical profiles, and diagnostic categories. Descriptive statistics summarize characteristics. The Shapiro-Wilk test evaluates normality. ROC curves and Youden's J index ascertain pfADA's optimal cut-off. Diagnostic performance measures pfADA against GeneXpert TB/MTB and TB culture.

Results:

Out of 660 cases, researchers extensively reviewed 146. The mean age was 45 years, with pfADA exhibiting a notable difference in various diagnostic categories. Sensitivity, Specificity, Positive Predictive Value (PPV), and Negative Predictive Value (NPV) stood at 82.08%, 92.40%, 90.16%, and 85.66% respectively, signifying its aptitude in diagnosing TPE and affirming its precision in excluding non-TB cases. Furthermore, the Optimal cut-off value of the Data identified was 47.2U/L.  Stratifying by age, the study affirmed other studies that age 45 and above calls for a lower cut-off value at 25.2U/L (sensitivity 72.34% and Specificity 80.95%, respectively).  The study also showed that retreatment cases of tuberculosis point to a higher cut-off value at 94U/L (sensitivity 88.89 and 48.08, respectively).  However, the population for these cases is limited and should be verified further by a larger population.

Conclusion:

The optimum cut-off value for pfADA, especially among the Filipino population, is 47.2U/L. The study justifies pfADA's diagnostic performance in TB pleural effusion. The findings align with existing literature, highlighting pfADA's potential as a dependable TPE marker. However, given the study's single-center nature and limited sample size, broader multi-center validations are advocated for enhanced generalizability.