The Role of Procalcitonin and C-Reactive Protein in Prediction of Etiology of Bloodstream Infections

Introduction: Inflammatory indicators such as procalcitonin (PCT) and C-reactive protein (CRP) may vary depending on the etiology of bloodstream infections. In this study, we aimed to investigate the role of serum PCT and CRP levels in predicting etiology in bloodstream infections. Methods: Blood cultures sent to our hospital's microbiology laboratory between January 2018 and July 2021 were retrospectively evaluated, and 501 patients with positive blood cultures were included in the study. According to blood culture growth, the patients were divided into Gram-negative bacteria (GNB), Gram-positive bacteria (GPB), fungus, Enterobacterales, and non-fermenter groups. We investigated whether there was a significant difference in the PCT and CRP values between the groups. Student's t-test was used to compare normally distributed numerical data, and the Mann-Whitney U test was used to compare non-normally distributed numerical data. The median value for continuous variables in each group was given as the first quartile (Q1) and third quartile (Q3). A comparison of categorical data was done with chi 2 test. Results: The PCT median value was found to be significantly higher in the GNB group compared with the GNB-GPB group. There was no significant difference between any of the groups for the CRP median value. In the GNB-GPB group comparison, the area under the curve for PCT cut-off value of 0.5 ng/mL was found to be 0.675 in the ROC curve (95% confidence interval=0.623-0.726; p<0.001), and the optimal cut-off value was found to be 1.45 ng/mL with 75% sensitivity, 53% specificity. Conclusions: Procalcitonin was found to be a marker that can be used to differentiate Gram-negative bacteremia from Gram-positive bacteremia. We concluded that CRP cannot be used to predict the etiology of bacteremia.