Biochemical characteristics of malignant pleural effusions

Introduction: Malignant pleural effusions (MPE) represent a common complication of advanced malignancies and are typically characterized as exudates. The aim of this study was to analyze the biochemical characteristics of MPE, with special emphasis on the application of Light's criteria and the serum-pleural albumin gradient (SPAG), as well as to assess potential discrepancies between these diagnostic approaches. Methods: This retrospective study included 49 patients with pleural effusion associated with malignancy, treated from January 2025 to January 2026. The malignant nature of pleural effusion was confirmed either cytologically or based on radiological evidence of pleural invasion. Biochemical parameters of pleural fluid and serum were analyzed, including proteins, albumin, lactate dehydrogenase (LDH), glucose, creatinine, and cholesterol. Effusions were classified according to Light's criteria and SPAG. Results: The majority of patients had lung tumors (61%), with a mean age of 70.9 ± 10.5 years. Biochemical analysis revealed an exudative profile, with a mean pleural fluid/serum protein ratio of 0.615 ± 0.117 and LDH ratio of 1.864 ± 1.323. According to Light's criteria, 96% of effusions were classified as exudates. In contrast, SPAG classified 20% of effusions as transudates. The mean SPAG value was 10.87 ± 4.31 g/L. Conclusion: Malignant pleural effusions predominantly exhibit biochemical characteristics of exudates, although with considerable variability in certain parameters. The observed discrepancy between Light's criteria and SPAG highlights the need for careful interpretation of biochemical findings and a broader diagnostic approach in the evaluation of MPE.