Identifying Malignant Pleural Effusion by A Cancer Ratio (Serum LDH: Pleural Fluid ADA Ratio)

AIM: We studied the diagnostic potential of serum lactate dehydrogenase (LDH) in malignant pleural effusion. METHODS: Retrospective analysis of patients hospitalized with exudative pleural effusion in 2013. RESULTS: Serum LDH and serum LDH: pleural fluid ADA ratio was significantly higher in cancer patients presenting with exudative pleural effusion. In multivariate logistic regression analysis, pleural fluid ADA was negatively correlated 0.62 (0.45–0.85, p = 0.003) with malignancy, whereas serum LDH 1.02 (1.0–1.03, p = 0.004) and serum LDH: pleural fluid ADA ratio 0.94 (0.99–1.0, p = 0.04) was correlated positively with malignant pleural effusion. For serum LDH: pleural fluid ADA ratio, a cut-off level of >20 showed sensitivity, specificity of 0.98 (95 % CI 0.92–0.99) and 0.94 (95 % CI 0.83–0.98), respectively. The positive likelihood ratio was 32.6 (95 % CI 10.7–99.6), while the negative likelihood ratio at this cut-off was 0.03 (95 % CI 0.01–0.15). CONCLUSION: Higher serum LDH and serum LDH: pleural fluid ADA ratio in patients presenting with exudative pleural effusion can distinguish between malignant and non-malignant effusion on the first day of hospitalization. The cut-off level for serum LDH: pleural fluid ADA ratio of >20 is highly predictive of malignancy in patients with exudative pleural effusion (whether lymphocytic or neutrophilic) with high sensitivity and specificity.