Pleural fluid biomarkers: a narrative review

Pleural fluid is a source from which various biomarkers can be obtained and measured to facilitate the management and prognostication of various conditions. This narrative review aims to summarise a few selected applications of pleural fluid biomarker analysis based on the latest literature.

A literature search for articles published in English regarding human subjects from the period January 2000 to December 2023 was performed through PubMed. Publications considered by the authors to be relevant were included in this review, with additional references added based on the authors' judgement. This review considered both prospective and retrospective cohort studies analysing the clinical value of a range of pleural fluid biomarkers.

The biomarkers selected in this narrative review have either established clinical applicability or promising initial results which require further research. Pleural fluid adenosine deaminase, mesothelin and N-terminal pro-B-type natriuretic peptide can optimize the diagnosis of tuberculous pleuritis, malignant mesothelioma and heart failure-related pleural effusion respectively. The detection rate for epidermal growth factor receptor mutations for lung cancer is higher in the pleural fluid than in the pleural tissue or plasma. Suitable targeted therapy in patients with detectable mutations can offer survival benefits. The pleural fluid neutrophil-lymphocyte ratio, soluble urokinase plasminogen activator receptor and plasminogen activator inhibitor 1 carry prognostic implications and can potentially guide subsequent treatment decisions. These biomarkers used individually, or in conjunction with other clinical parameters, should only be utilised in pre-defined, appropriate clinical conditions to maximize their clinical value.

A great variety of different biomarkers are available for analysis in pleural fluid. Further research and development are necessary to widen the spectrum and enhance the clinical utility of pleural fluid biomarkers. Comparison with the diagnostic utilities of serum biomarkers and other investigation parameters, such as radiological findings, could be considered when evaluating the performance of pleural fluid biomarkers.