Background Tuberculous pleural effusion (TPE) is a common extrapulmonary manifestation of tuberculosis and poses significant diagnostic challenges due to its paucibacillary nature. Measurement of pleural fluid adenosine deaminase (ADA) is widely used as a supportive diagnostic marker; however, elevated ADA levels may also be observed in other inflammatory and malignant conditions, thereby limiting its specificity. Since tuberculous pleural effusion is predominantly mediated by a cell-mediated immune response, particularly involving activated T lymphocytes, the cellular composition of pleural fluid may provide additional diagnostic value. The lymphocyte-to-neutrophil ratio reflects this immune response and may enhance diagnostic accuracy when used alongside ADA estimation. Aim and Objectives To evaluate the diagnostic utility of pleural fluid adenosine deaminase levels in combination with the lymphocyte-to-neutrophil ratio for the diagnosis of tuberculous pleural effusion. Materials and Methods This prospective observational study was conducted at Sree Mookambika Institute of Medical Sciences, Tamil Nadu, India, from December 2023 to November 2024. A total of 150 patients with exudative pleural effusion were enrolled. Pleural fluid samples were obtained under aseptic precautions and subjected to biochemical analysis, including ADA estimation, and cytological examination for differential leukocyte counts. The diagnostic performance of ADA alone and in combination with the lymphocyte-to-neutrophil ratio was analyzed using standard statistical methods. Results At a cut-off value of ≥40 U/L, pleural fluid ADA demonstrated a sensitivity of 94.6%, specificity of 94.8%, positive predictive value of 96.6%, negative predictive value of 91.7%, and an overall diagnostic accuracy of 94.6%, which was statistically significant (p < 0.001). When combined with a lymphocyte-to-neutrophil ratio of ≥0.75, diagnostic performance improved further, yielding a sensitivity of 96.7%, specificity of 100%, positive predictive value of 100%, negative predictive value of 95.1%, and an overall accuracy of 98%. Conclusion Pleural fluid adenosine deaminase is a highly sensitive marker for the diagnosis of tuberculous pleural effusion. The addition of the lymphocyte-to-neutrophil ratio significantly enhances diagnostic accuracy and specificity compared to ADA estimation alone. The combined use of these parameters provides a reliable, cost-effective, and non-invasive approach for the diagnosis of tuberculous pleural effusion, particularly in resource-limited settings.

Adenosine deaminase; Tuberculous pleural effusion; Lymphocyte-neutrophil ratio; Pleural fluid analysis; Tuberculosis