Study of Cancer Ratio (Serum Lactate Dehydrogenase/Pleural Fluid Adenosine Deaminase) in Malignant Pleural Effusion

Objectives Malignant pleural effusion (MPE) is a frequent cause of exudative pleural effusion and often indicates advanced malignancy with poor prognosis. Although pleural fluid cytology remains the diagnostic reference standard, its sensitivity is limited. The cancer ratio, defined as the ratio of serum lactate dehydrogenase (LDH) to pleural fluid adenosine deaminase (ADA), has been proposed as a simple and inexpensive biomarker to differentiate malignant from non-malignant pleural effusions. This study aimed to evaluate the diagnostic performance of the cancer ratio (serum LDH/pleural fluid ADA) for predicting MPE in patients with exudative pleural effusion. Material and Methods This cross-sectional observational study was conducted from April 2021 to September 2022 at a tertiary care centre in Mangaluru, India. Fifty-six adult patients with exudative pleural effusion diagnosed using Light’s criteria were included. Pleural fluid ADA and serum LDH levels were measured using standard enzymatic assays. The cancer ratio was calculated as serum LDH divided by pleural fluid ADA. Pleural fluid cytology served as the diagnostic reference for malignancy. Receiver operating characteristic (ROC) curve analysis was performed to determine diagnostic accuracy, including sensitivity, specificity, and area under the curve (AUC). Results The mean age of the study population was 58.38 ± 11.84 years, and 62.5% were male. Malignancy was detected in 46 patients (82.1%) by pleural fluid cytology, with lung adenocarcinoma being the most common underlying malignancy. The mean pleural fluid ADA was 11.35 ± 8.61 U/L, the mean serum LDH was 582.70 ± 696.14 U/L, and the mean cancer ratio was 182.46 ± 700.84. ROC analysis demonstrated an AUC of 0.526 for the cancer ratio (cut-off: 30.65; sensitivity 71.7%, specificity 50.0%), indicating limited discriminative ability. Serum LDH showed better diagnostic performance (AUC 0.707; sensitivity 67.4%, specificity 60.0%) and was the only parameter significantly associated with MPE ( p = 0.042). Conclusion In this cohort, the cancer ratio demonstrated limited diagnostic accuracy for predicting MPE and did not show a statistically significant association with malignancy. Serum LDH showed comparatively better diagnostic performance. The cancer ratio should therefore be considered an exploratory biomarker, and larger multicentric studies are required to further evaluate its potential role in the diagnostic evaluation of exudative pleural effusion.