Combined Analysis of C-reactive Protein in Pleural Fluid and Serum is Effective in the Differential Diagnosis of Exudative Pleural Effusions
Abstract Background: Exudative pleural effusion (EPE) is one of the common pleural manifestations of various diseases. Differential diagnosis of EPE is imperative clinically as it identifies different causes of EPE, thereby, providing effective treatments. Thoracoscopy is a useful tool for differential diagnosis of EPE. However, some patients would refuse thoracoscopic examination due to its invasive nature. In addition, the specificity and sensitivity of existing routine tests of EPE are less satisfying. Therefore, there is a great need to establish an effective method for differential diagnosis of EPE.Methods: This study was a single-institution retrospective analysis of diagnostic efficiency of C-reactive protein (CRP) and procalcitonin (PCT) between March 2018 and September 2018. Eighty-seven patients diagnosed with EPE were enrolled. All patients underwent diagnostic thoracentesis. And the EPE was examined using biochemical, routine, microbiological, and cytological methods. Pathological cytology detection was of necessity for those with the suspicion of malignant PE. Benign PE comes from patients with pneumonia, empyema and tuberculosis. The levels of CRP and PCT of EPE and serum were measured before the treatment. Correlation analysis and receiver-operating characteristic (ROC) curve analysis were conducted to determine the underlying relationship between levels of CRP and PCT, and differential diagnosis.Results: Receiver operating characteristic analysis showed that the sensitivity and specificity for the analysis of pleural fluid CRP (p-CRP) are higher (cut-off: 17.55 pg/mL; sensitivity: 75.00 %, specificity: 83.90%) than that of serum CRP (s-CRP, cut-off: 23.90 pg/mL; sensitivity: 71.00 %, specificity: 80.4%) in the differential diagnosis for EPE. However, the analysis of pleural fluid PCT (p-PCT) and serum PCT (s-PCT) didn’t demonstrate correlations with EPE. Combined analysis of p-CRP (cut-off: 17.55 mg/dL) with s-CRP (cut-off: 23.9 pg/mL) showed the highest diagnostic accuracy (88.4%) in diagnosing infectious EPE.Conclusions: The data support the close relationship between combined analysis of p-CRP with s-CRP and effective and accurate differential diagnosis of EPE, due to its higher sensitivity and specificity. However, as a highly sensitive marker to diagnose bacterial infections, neither s-PCT nor p-PCT, showed correlations with the differential diagnosis of EPE.