Serum C-Reactive Protein as an Adjunct for Identifying Complicated Parapneumonic Effusions

Distinguishing non-purulent complicated parapneumonic pleural effusions (CPPE) from uncomplicated parapneumonic pleural effusions (UPPE) is challenging. We aimed to determine whether serum C-reactive protein (sCRP), alone or in combination with classical pleural fluid parameters, is useful in making such discrimination. The study was composed of a total of 104 consecutive patients, of whom 47 had UPPE and 57 had CPPE. Standard biochemical pleural fluid data along with sCRP were measured. sCRP at the time of thoracentesis or chest tube insertion was significantly higher in CPPE (238 mg/L) than UPPE (147 mg/L). At the optimum cutoff value of 200 mg/L, sCRP had a sensitivity, specificity, likelihood ratio positive, likelihood ratio negative, and area under the receiver-operating characteristic curve for diagnosing CPPE of 58 %, 81 %, 3.1, 0.52, and 0.67, respectively. The combination of sCRP > 200 mg/L with pleural fluid glucose < 60 mg/dL using an "and" rule achieved a specificity of 98 %, whereas both parameters combined in an "or" rule had a sensitivity of 81 %, which was higher than that of pleural fluid pH (57 %) or glucose (54 %). sCRP, when combined with classical pleural fluid biochemistries, improves the diagnostic accuracy in identifying those patients with non-purulent parapneumonic effusions who need chest drainage.