Qian Yang,1,2,* Su-Na Cha,1,2,* Yan Niu,3 Jian-Xun Wen,3 Li Yan,2,4 Ling Hai,5,6 Ying-Jun Wang,1,2 Wen-Hui Gao,1 Feng Zhou,7 Qianghua Zhou,8 Zhi-De Hu,1,2 Wen-Qi Zheng1,2 

1Department of Laboratory Medicine, The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, People’s Republic of China; 2Key Laboratory for Biomarkers, Inner Mongolia Medical University, Hohhot, People’s Republic of China; 3Medical Experiment Center, The College of Basic Medicine, Inner Mongolia Medical University, Hohhot, People’s Republic of China; 4Department of Respiratory and Critical Care Medicine, The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, People’s Republic of China; 5Department of Pathology, The College of Basic Medical, Inner Mongolia Medical University, Hohhot, People’s Republic of China; 6Department of Pathology, The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, People’s Republic of China; 7Department of Blood Transfusion, The Affiliated Hospital of Inner Mongolia Medical University, Hohhot, People’s Republic of China; 8Department of Laboratory Medicine and Pathobiology, Temerty Faculty of Medicine, University of Toronto, Toronto, Canada

*These authors contributed equally to this work

Correspondence: Zhi-De Hu, Email hzdlj81@163.com; Wen-Qi Zheng, Email zhengwenqi2011@163.com

Introduction: The diagnostic utility of pleural fluid C-reactive protein (CRP) and procalcitonin (PCT) for parapneumonic pleural effusion (PPE) is a subject of ongoing investigation. There remains lack studies comparing their diagnostic accuracy in a head-to-head manner. Furthermore, the incremental diagnostic value of their combination over a single marker and the net benefit of them remains unknown.
Methods: This prospective study enrolled participants presenting with undiagnosed pleural effusion, subsequently measuring their pleural levels of CRP and PCT. A diagnostic model that integrated both biomarkers was constructed using logistic regression analysis. The diagnostic performance and net benefit of CRP, PCT, and the composite model were assessed through receiver-operating characteristic (ROC) curve analysis and decision curve analysis (DCA).
Results: The study included 32 PPE patients and 121 patients without PPE. The area under the ROC curve (AUC) for CRP was 0.73 (95% confidence interval [CI]: 0.63– 0.83), with a sensitivity of 0.71 (95% CI: 0.55– 0.87) and a specificity of 0.68 (95% CI: 0.59– 0.77) at a threshold of 10 mg/L. In contrast, the AUC for PCT was 0.58 (95% CI: 0.46– 0.69), with sensitivity and specificity rates of 0.50 (95% CI: 0.33– 0.67) and 0.65 (95% CI: 0.56– 0.74) at a threshold of 0.1 ng/mL, respectively. Notably, the AUC for the diagnostic model was comparable to that of CRP alone at 0.73 (95% CI: 0.63– 0.82). DCA showed that applying CRP provided a net clinical benefit, while PCT did not.
Conclusion: Pleural fluid CRP possesses moderate diagnostic capability for PPE, while PCT exhibits limited diagnostic utility. Additionally, the combined application of CRP and PCT does not confer any significant enhancement in diagnostic accuracy over the use of CRP alone.

Keywords: C-reactive protein, diagnostic test accuracy, parapneumonic pleural effusion, procalcitonin