Etiological profile of pleural effusion in Gujarat, India: A prospective observation study at a tertiary care centre

Background: Pleural effusion is a common clinical entity with a broad etiological spectrum, including infectious, malignant, and systemic causes. Accurate differentiation between transudative and exudative effusions is essential for diagnosis and management. Although Light’s criteria remain the cornerstone of classification, adjunctive biochemical and microbiological parameters may improve diagnostic accuracy, particularly in India, where tuberculosis remainshighly prevalent.Aim: To evaluate the etiological profile of pleural effusion using pathological, microbiological, and biochemical examination of pleural fluid, and to assessthe diagnostic utility of Light’s criteria and the serum–effusion albumin gradient (SEAG).Materials and Methods: This prospective observational study was conducted over 18 months at a tertiary care centre in Gujarat, India. A total of 140 adultpatients with radiologically confirmed pleural effusion were enrolled. All patients underwent clinical evaluation, pleural fluid biochemical analysis, cytology,adenosine deaminase (ADA), lactate dehydrogenase (LDH), acid-fast bacilli staining, CBNAAT, and paired serum testing. Effusions were classified usingLight’s criteria, and SEAG was evaluated as an adjunctive parameter.Results: Of the 140 patients, 95 (67.9%) were male, and the most affected age group was 41–50 years (36/140, 25.7%). Exudative effusions constituted122/140 cases (87.1%), whereas 18/140 (12.9%) were transudative. Among exudative effusions, tuberculosis was the most common aetiology (48/122,39.3%), followed by para-malignant effusions (30/122, 24.6%) and malignant effusions (23/122, 18.9%). ADA levels >40 U/L identified 36/48 (75.0%) casesof tuberculous pleural effusion, whereas CBNAAT was positive in 6/48 (12.5%). LDH was elevated in 110/140 patients (78.6%) and was more frequentlyassociated with exudative effusions. Light’s criteria showed excellent sensitivity for identifying exudates; however, 2 patients with cardiac effusions weremisclassified as exudates, corresponding to an overall misclassification rate of 1.4% (2/140). SEAG >1.2 g/dL helped identify these pseudo-exudates,although overlap with true exudative effusions limited its standalone value.Conclusion: Exudative pleural effusion was the predominant type in this cohort, with tuberculosis as the leading aetiology. Light’s criteria remain highlysensitive for initial classification, but a small proportion of cardiac transudates may be misclassified. ADA is a useful marker for tuberculous pleuraleffusion, whereas CBNAAT has low sensitivity in pleural fluid. SEAG may serve as a useful adjunct in selected cases but should not replace standardbiochemical criteria. A multimodal diagnostic approach integrating clinical, biochemical, cytological, and microbiological findings remains essential foraccurate etiological diagnosis.