The Usefulness of Pleural Fluid ADA to Serum CRP Ratio in Differentiating between Tubercular and Malignant Pleural Effusion

Background: Tubercular pleural effusion (TPE) and malignant pleural effusion (MPE) are usually distinguished by pleural fluid cellular predominance, cytology and adenosine deaminase (ADA) level although both diseases may show similar cytological and biochemical picture including ADA. In such cases, differentiating TPE and MPE is challenging and needs histopathology of pleural tissue following closed needle biopsy of pleura, pleuroscopy, VATS (Video Assisted Thoracoscopic surgery). Unfortunately, diagnostic yield of closed needle pleural biopsy is not satisfactory and latter procedures are not widely practiced. Objective: To assess the usefulness of pleural fluid ADA to serum CRP ratio in differentiating between tubercular and malignant pleural effusion. Materials and Methods: This cross-sectional, method validation study was conducted in the National Institute of Diseases of the Chest and Hospital (NIDCH), Mohakhali, Dhaka from July 2021 to September 2022 on diagnosed case of tubercular pleural effusion (TPE) and malignant pleural effusion (MPE). Ratio of pleural fluid ADA to serum CRP was estimated in all cases and compared between patient with TPE and MPE. A receiver operating characteristic curve (ROC) was constructed for identifying TPE. A value of p<0.05 was considered statistically significant for all tests. Results: A total of 59 patients were enrolled in this study, of which 31 patients had TPE and 28 patients had MPE. Pleural fluid ADA level was significantly higher in patient with TPE but there was no significant difference in serum CRP level between patients with TPE and MPE. Pleural fluid ADA to serum CRP ratio was also higher in TPE group compared to MPE group and the difference was statistically significant. At cut off value of e”1.28, pleural fluid ADA to serum CRP ratio had a sensitivity of 90.3%, specificity of 82.1%, accuracy of 86.4%, positive predictive value of 84.8%, negative predictive value of 88.5%, positive likelihood ratio of 5.06 and negative likelihood ratio of 0.12 in diagnosis of TPE and area under curve (AUC) was 0.921 on receiver operating characteristic curve (ROC). Conclusion: This study demonstrated that pleural fluid ADA to serum CRP ratio was significantly higher in tubercular pleural effusion comparing with malignant pleural effusion. Chest Heart J. 2023; 47(1) : 40-48