Introduction: In contrast to tuberculous pleurisy (TP), no accurate and commonly accepted biochemical marker of malignant pleural effusion (MPE) has been established.

Objectives: We aimed to evaluate the ability of a previously reported cancer ratio (CR) to discriminate between MPEs and non–MPEs; to test whether age may have additional value in differentiating MPEs from non–MPEs; and if so, to combine lactate dehydrogenase (LDH) and age with other TP biomarkers in search of an index useful in the identification of MPEs.

Patients and methods: A retrospective analysis of data from 140 patients with malignant (n = 74), tuberculous (n = 37), and parapneumonic (n = 29) pleural effusions was performed. The diagnostic performance of a test to discriminate between MPEs and non–MPEs was evaluated using the receiver operating characteristic curve analysis.

Results: Three ratios showed the largest area under the curve (AUC): serum LDH to pleural fluid soluble Fas ligand, age to pleural fluid adenosine deaminase (ADA), and serum LDH to pleural fluid interleukin 18; moreover, the ratios were characterized by high sensitivity (95%, 93.2%, and 92.9%, respectively) and fair specificity (64.8%, 71.2%, and 58.5%, respectively) for differentiating MPEs from non–MPEs. The AUC for CR was lower and showed a sensitivity of 94.6% and a specificity of 68.2%.

Conclusions: Our study showed a lower specificity of the CR for discriminating between MPEs and non–MPEs than previously reported. We demonstrated that the combinations of serum LDH with other pleural fluid biomarkers of TP have a similar diagnostic performance. We also found that age might be an important factor differentiating between MPEs and non–MPEs and proposed a new age to pleural fluid ADA ratio which has a discriminative potential similar to that of the CR.