A Study Investigating Markers in PLeural Effusion (SIMPLE): a prospective and double-blind diagnostic study

INTRODUCTION: Serum and fluid laboratory markers are valuable for exploring the aetiologies of pleural effusion (PE) because of their relative non-invasiveness, low cost, objective result and short turnaround time. The diagnostic accuracy of these potential markers needs to be rigorously evaluated before their widespread application in clinical practice. Here, we plan to perform a Study Investigating Markers in PLeural Effusion (SIMPLE). METHODS AND ANALYSIS: This is a prospective and double-blind clinical trial which is being performed at the Affiliated Hospital of Inner Mongolia Medical University, China. Adult patients admitted for the evaluation of aetiology of PE from September 2018 to July 2021 will be enrolled after informed consent. Pleural fluid and serum specimens will be collected and stored at –80°C for the laboratory analysis. The final diagnosis will be concurred with further imaging, microbiology, cytology and biopsy if needed. The results of investigated laboratory markers will be unknown to the clinicians who will make diagnosis and the clinical diagnoses will be unknown to the laboratory technicians who will determine markers. The diagnostic accuracy of investigated markers will be assessed using receiver operating characteristics (ROC) curve analysis, multivariable logistic regression model, decision curve analysis (DCA), net reclassification index (NRI) and integrated discriminatory index (IDI). ETHICS AND DISSEMINATION: The study is approved by the Ethic Committee of the Affiliated Hospital of Inner Mongolia Medical University (NO: 2018011). The results of SIMPLE will be submitted to international scientific peer-reviewed journals or conferences in laboratory medicine or respiratory medicine, thoracic diseases. TRIAL REGISTRATION NUMBER: Chinese Clinical Trial Registry (ChiCTR1800017449); Pre-results.