Role of pleural fluid C-reactive protein in distinguishing different causes of pleural effusions

Background
Pleural effusion (PE) is a common condition, and determining its cause can be difficult. Various criteria, such as Light’s criteria and Heffner criteria, are used to differentiate between transudative and exudative PE and to identify the underlying causes of exudative PE. This study aimed to evaluate the effectiveness of pleural C-reactive protein (CRP) in distinguishing between transudative and exudative PE, as well as differentiating among the various causes of exudative PE.


Patients and methods
A prospective cross-sectional research has been performed at Ain Shams University hospital where 73 patients underwent ultrasound-guided thoracocentesis. PE was categorized into transudates and exudates as defined by Light’s criteria. The pleural fluid (PF) sample was analysed for CRP, Pleural CRP (pCRP) to serum CRP (sCRP) ratio, and serum to pleural gradient were all calculated and compared.


Results
The mean age of the cases was significantly lower in exudative than in transudative effusions. pCRP and pleural to sCRP ratio were significantly lower in transudates than exudates. There was no statistical significance regarding serum to pleural gradient in differentiating between transudates and exudates. pCRP did not statistically differentiate between malignant, parapneumonic effusion and empyema. The pCRP in parapneumonic and empyema were higher but not statistically significant. Pleural to sCRP ratio was lower in malignant effusions than infectious effusions, however, without statistical significance.


Conclusion
Serum CRP, PF CRP, and their ratio illustrated statistically significant differentiation among transudates and exudates but serum pleural gradient did not. Pleural CRP values and serum to pleural CRP gradient were greater in empyema and parapneumonic than malignant effusion but without statistical significance. PF CRP cut off value was 25 mg/l in differentiating transudates from exudates.