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

Abstract

Background: Exudative pleural effusion is a common problem and tissue diagnosis is the gold standard for the diagnosis but it is invasive procedure with complications. In contrast to tuberculous pleurisy (TP), no accurate and commonly accepted biochemical marker of malignant pleural effusion (MPE) has been established. We studied the diagnostic potential of serum lactate dehydrogenase (LDH): pleural fluid ADA ratio (Cancer ratio) to identify malignant pleural effusion.

Aim : To determine the diagnostic utility of cancer ratio (serum LDH/fluid ADA)  to differentiate malignant from non-malignant exudative  pleural effusion.

Materials and Methods : A cross sectional study of 70 patients (21 women/ 49 men) diagnosed with exudative pleural effusion (49 patient with malignant, 21 patient with non-malignant pleural effusion) at Al-Assad and Al-Mouassat University Hospitals, Damascus, Syria during the period between 2020 - 2021.

ADA levels were measured on pleural fluid obtained by thoracocentesis and serum LDH levels were measured within 24 hours from thoracocentesis. Cancer ratio (serum LDH/fluid ADA) was calculated, receiver operating characteristics curve (ROC) analysis was applied to estimate their discriminative properties, and Youden Index by MedCalc 20.009 was used to determine the best cut-off value of Cancer ratio and its sensitivity and specificity.

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 with malignancy, whereas serum LDH and serum LDH: pleural fluid ADA ratio was correlated positively with malignant pleural effusion (p value was 0.0001 for each).

For serum LDH: pleural fluid ADA ratio, a cut-off level of ≥ 83.9 showed sensitivity, specificity of 75.51%  and 90.48%, respectively. The positive predictive value 94%, negative predictive value 61%, positive likelihood ratio was 7.9, while the negative likelihood ratio at this cutoff was 0.27. the AUC was 0.897.

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 83.9 is highly predictive of malignancy in patients with exudative pleural effusion (whether lymphocytic or neutrophilic)

with high sensitivity and specificity.