Prognostic value of C-reactive protein in parapneumonic effusions

Background and objective: Parapneumonic effusions (PPE) that require drainage are referred to as complicated parapneumonic effusions (CPPE). Following resolution of these effusions, residual pleural thickening (RPT) may persist. We hypothesize that the concentrations of CRP in pleural fluid (CRP_pf) and serum (CRP_ser) can be used to identify CPPE and to predict RPT. Methods: All patients with non‐purulent PPE, who were admitted to two tertiary hospitals during a 30‐month period, were enrolled in the study. Baseline CRP_pf and CRP_ser levels were compared between patients with complicated or uncomplicated PPE, as well as between patients with or without RPT of >10 mm, 6 months after discharge from hospital. Cut‐off values for identification of CPPE and prediction of RPT were determined by receiver operating characteristic curve analysis. Logistic regression analysis was performed to assess the association between CRP levels and RPT. Results: Fifty‐four patients were included in the study. Patients with CPPE (n = 23) had significantly higher levels of both CRP_pf and CRP_ser than those with uncomplicated PPE. For identification of CPPE, a CRP_pf level >78.5 mg/L and a CRP_ser level >83 mg/L gave 84% and 47% sensitivity, with 65% and 87% specificity, respectively. Classical criteria (pleural fluid pH <7.20, LDH >1000 IU/L, glucose <600 mg/L) were superior for this purpose. A combination of classical biomarkers with CRP levels using an ‘AND’ or ‘OR’ rule improved the positive and negative predictive values, respectively. CRP_ser was an independent predictor for development of RPT (adjusted OR 1.18). A CRP_ser level >150 mg/L had 91% specificity and 61% sensitivity for prediction of RPT. Conclusions: This study demonstrated the value of CRP_ser for prediction of RPT in patients with PPE. Moreover, when used in combination with classical biomarkers, CRP levels may be a useful adjunct for decision‐making in relation to treatment of patients with non‐purulent PPE.