Diagnostic value of pleural and serum CRP levels in patients with pleural effusion

Pleural effusion defined as fluid accumulation between pleural leaves is a common pathology in the clinical practice of chest diseases. Although the diagnosis of pleural effusion is easy, determining the etiology is sometimes difficult. While performing differantial diagnosis, it is necessary to apply to many laboratories and imaging methods, so sometimes time is lost. Recently, various biomarkers have been the subject of research in the etiology and differential diagnosis of pleural effusion. In our study, we aimed to examine the diagnostic value of CRP, an acute phase protein, in pleural effusion. This study was carried out by prospectively examining 103 patients with pleural effusıon who were hospitalized in Gazi Unıversity Medical Faculty Hospital Chest Diseases Department and detected in the outpatient clinic between April 2018 and June 2020. 4 patients were excluded from the study due to the follow up and cause of pleural effusion couldn't be found. Those who couldn't undergo diagnostic thoracentesis and those under 18 years of age were not included in the study. In 19 patients, it was classified separately because there was an additional disease that would cause high CRP. The remaining 80 patients were grouped according to their diagnosis as empyema (5), parapneumonic effusion (6), heart failure (9), malignant pleural effusion (11), paramalignant effusion (20), tuberculous pleurisy (8), others (21) and the diagnostic value of CRP levels in serum was investigated.Pleural fluid CRP (Pl CRP) levels were higher in empyema and parapneumonic effusion compared to heart failure (p<0,01) and parapneumonic effusion compared to malignant and paramalign effusion (p<0,01). CRP levels measured in serum were higher in empyema and parapneumonic effusion compared to heart failure (p<0,01), parapneumonic effusion compared to malignant effusion, paramalign effusion, tuberculous pleurisy and others groups (p<0,01). When looking at the pleural fluid CRP /serum CRP ratio, no significantdifference was found between the groups in terms of values measured in both pleura and serum (p=0,21). When the patients were divided into two groups as those with pleural infection, pleural CRP and serum CRP levels were hidher in the group with pleural infection (p<0,01). When the patients were divided into two groups as pleural effusion due to malignancy and those not due to malignancy, no significant was found in the levels of Pl CRP, serum CRP, Pl CRP/Serum CRP (p=0,16, p=0,35, p=0,36). All values of Pl CRP, Serum CRP, Pl CRP/Serum CRP, which were checked fort he differantiation of exudate and transudate, were found to be higher in the exudate group than in the transudate group (p<0,01, p=0,02, p<0,01,). In Spearman's correlation analysis, which was examined between serum and pleural CRP levels in all patients included in the study, it was found that pleural fluid and serum CRP levels showed a strong positive correlation (p<0,01) (r= 0,838). When the Pl CRP cut off is taken as 37,5 in the differantiation of exudate and transudate, the sensitivity %51, specificity %91 and AUC 0,71 (%95 CI). In the differantiation of infectious and non-infectious pleurisy, when the Pl CRP cut off level was taken as 78, the sensitivity %57 and the specificity %88, AUC 0,75 (%95 CI). Neutrophil predominance in pleural fluid was detected when Pl CRP (p<0,01, x2 = 9,8). In conclusin, in our study, it was found that pleural fluid and serum CRP levels showed strong positive correlation with each other regardless of the cause of pleural effusion and we determined that pleural fluid CRP levels were significant in differentiating infectious and non-infectious effusion, distinguishing exudate transudate, and differentiating parapneumonic effusion, heart failure, malignant, paramalign effusion. It was not statistically significant in differentiating malignant and non-malignant pleural effusion. Keywords: pleural effusion, CRP, diagnosis, empyema, heart failure, parapneumonic effusion, malignant effusion, tuberculous pleurisy