Diagnostic value of pleural fluid and serum C-reactive protein/albumin ratio in exudate/transudate, infectious/non-infectious pleural fluid discrimination.

As a new parameter, the C-reactive protein (CRP)/albumin ratio (CAR) has been shown to be more accurate than CRP and albumin alone in predicting the diagnosis and overall prognosis in cancer, sepsis, and vascular and non-vascular conditions. In this direction, we aimed to investigate the role of CAR in the differentiation of transudate/exudate and infectious/non-infectious in our study. A total of 160 patients who were examined for pleural fluid between August 2020 and February 2021 were included in our single-center prospective observational study. The study did not include those who could not undergo diagnostic thoracentesis and those under the age of 18. The presence of pleural effusion was determined by physical and radiological examinations [chest radiograph, thorax computed tomography, thoracic ultrasonography (US)]. Diagnostic thoracentesis was performed under the guidance of thoracic US after the patients who met the inclusion criteria signed an informed consent form. A total of 160 patients, 117 (73.1%) male and 43 (26.9%) female, were included in the study. While exudate was detected in 101 (63.1%) cases and transudate was detected in 59 (36.9%) cases, 47 (29.4%) of these were due to infectious and 113 (70.6%) non-infectious causes. The mean pleural fluid CAR (46.38) and serum CAR (72.43) in the infectious group were found to be significantly higher than those in the non-infectious group (13.17 and 19.48, respectively) (p<0.001). The pleural fluid and serum CAR (31.79 and 49.68) were found to be significantly higher in the exudate-qualified group compared to the transudate-qualified group (7.76 and 9.97) (p<0.001). When the threshold value for the pleural fluid CAR is >15.65, it is 80.9% sensitive and 73.5% specific in predicting infectious fluid; when the threshold value was >9.48, it was found to be 71.3% sensitive and 71.2% specific in exudate-transudate discrimination. In conclusion, in our study, we see that the pleural fluid and serum CAR are promising parameters in the differentiation of infectious/non-infectious pleural effusions and in the differentiation of exudate/transudate.