Relations between serum and pleural fluid biomarkers: a new look of an old concept

Abstract

Background: Although cytological examination of pleural fluid samples can simply diagnose malignant pleural effusion (MPE), this test has many limitations. There are no established biomarkers for accurate diagnosis of MPE. This study investigated the association of serum lactate dehydrogenase (LDH)/pleural fluid adenosine deaminase (ADA) which is the cancer ratio with MPE together with assessment of the utility of combining pleural lymphocyte counts "cancer ratio plus" in diagnosing MPE and to evaluate the ability of these markers in differentiating MPE from tuberculous pleural effusion (TPE). Results: This prospective study included 150 individuals who were divided into 3 groups including malignant (n = 94), tuberculous (n = 31), and parapneumonic (n = 25) effusions. It was done during the period from January 2018 to July 2019 to assess the utility of cancer ratio and cancer ratio plus in discrimination between MPE and non-MPE. Serum LDH, cancer ratio, and cancer ratio plus were significantly associated with MPE. Also, age, cancer ratio, and serum LDH to pleural fluid lymphocyte count ratio were positive predictors of MPE. A cutoff level of > 16.02 for the cancer ratio showed sensitivity and specificity of 61% (95% CI 0.5002-0.7056) and 96% (95% CI 0.8769-0.9956) respectively. At this cutoff, the positive likelihood ratio was 16.99, while the negative likelihood ratio was 0.41. Conclusion: Cancer ratio was found to be more accurate than cancer ratio plus and serum LDH to pleural fluid lymphocyte count ratio in identifying MPE especially in patients with negative pleural fluid cytology.