Predictive Value of IL-6, PCT, NLR, and CRP in differentiating gram-negative bacterial bloodstream infections from gram-positive bacterial and fungal bloodstream infections in febrile patients

Identification of bloodstream infections (BSI) in patients with fevers is crucial for the timely implementation of specific and acute therapies, including early administration of antibiotics and source control. Many studies have evaluated the roles of biomarkers in diagnosing initial BSIs, distinguishing between BSIs caused by different sources and species of bacteria. The aim of the current study was to evaluate the diagnostic ability of interleukin-6 (IL-6), procalcitonin (PCT), neutrophil/lymphocyte ratio (NLR), and C reactive protein (CRP) in discriminating gram-negative (GN) bacterial infections from gram positive (GP) bacterial and fungal infections in febrile patients with BSIs. This retrospective study was conducted for a total of 567 patients with fevers at the Fever Clinic of the Chinese PLA General Hospital, between November 2015 and December 2017. Serum levels of IL-6, PCT, and CRP, as well as the NLR, were obtained from electronic medical records and compared between the GN-BSI group (n=188), GP-BSI group (n=168), Fungal BSI group (n=38), and culture negative group (n=173). Sensitivity (Se), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV), Youden index, and areas under the ROC curve (AUC) were determined, analyzing the diagnostic abilities of these biomarkers in discriminating between bloodstream infections caused by different pathogens. Results showed that IL-6 was useful in discriminating GN-BSI from GP-BSI and fungal-BSI. NLR was valuable in discriminating Fungal-BSI from GP-BSI in febrile patients. Utilization of these biomarkers to predict bloodstream infections caused by different pathogens requires further assessment, however, in future studies.