Diagnostic Efficacy of C-Reactive Protein in Differentiating Various Causes of Exudative Pleural Effusion: Disease Research Should Not Be Exclusive to the Wealthy.

Background and Objectives: Discrimination between various causes of exudative pleural effusion (PE) remains a major clinical challenge, and to date, definitive biochemical markers for this discrimination remain lacking. An increasing number of studies have reported that serum C-reactive protein (CRPs), pleural fluid CRP (CRPpf), and CRPpf/CRPs ratio (CRPr) are useful for the differential diagnosis of exudative PE; however, their efficacy rate is not similar in these studies. The majority of these studies were conducted on small groups of subjects, and the efficacy of the gradient between CRPs and CRPpf (CRPg-calculated as CRPs-CRPpf) in this differentiation has not been previously investigated. This study aims to evaluate the efficacy rate of CRPs, CRPpf, CRPg, and CRPr in the differential diagnoses of various causes of exudative PE in a relatively large cohort of patients. Materials and Methods: The research group included 282 subjects with exudative PE-146 had parapneumonic effusion (PPE), 126 had malignant pleural effusion (MPE), and 10 had tuberculous pleural effusion (TPE). The values are presented as mean ± SD. Results: The mean CRPs level was significantly higher in the PPE group compared to the MPE group (p < 0.0001) and the TPE group (p < 0.001), and also significantly higher in the TPE group than in the MPE group (p = 0.0009). Similarly, the mean CRPpf level was significantly higher in the PPE group than in the MPE group (p < 0.0001) and the TPE group (p = 0.04), and also significantly higher in the TPE group than in the MPE group (p < 0.0001). The mean CRPg level was significantly higher in the PPE group than in both the MPE group (p < 0.0001) and the TPE group (p < 0.002). The mean CRPr level did not differ significantly among these groups of exudate. Conclusions: CRPs, CRPpf, and CRPg are effective in the differential diagnosis of exudative PE, while CRPr was not effective in this regard. The main limitation of this study is that the sample size of the TPE group is very small.