Evaluation of the clinical diagnostic value of traditional inflammatory markers and novel biomarkers in intracellular bacterial bloodstream infections

The clinical symptoms of the patients with intracellular bacterial bloodstream infections (Intra-bac BSIs) are atypical, and no early and accurate diagnostic biomarkers exist, which can easily lead to misdiagnosis, inappropriate and delayed treatment. Therefore, it is imperative to find novel biomarkers to help clinical diagnosis of Intra-bac BSIs. The present study was initiated to evaluate the diagnostic values of traditional inflammatory biomarkers (PCT, WBC and NEU% in identifying the patients with Intra-bac BSIs, and to further explore into the possibility of using suPAR and sCD14-ST as novel biomarkers for Intra-bac BSIs. A multi-center retrospective study was conducted in three teaching hospitals in Chongqing. A total of 146 cases with BSIs, including 73 cases with Intra-bac BSIs and 73 cases with extracellular bacterial BSIs (Extra-bac BSIs) were enrolled in the retrospective study. We then prospectively enrolled 34 patients with Intra-bac BSIs, 34 patients with Extra-bac BSIs, 34 patients with viral infection and with normal medical examination results as a control group for further detection of sCD14-ST and suPAR by ELISA. PCT levels, WBC counts and NEU% in patients with Intra-bac BSIs were not increased or minimally increased, they were significantly lower than that with Extra-bac BSIs (P < 0.05), especially those with the Brucella bacterial BSIs, demonstrated a respective negative rate of 84% and 92% for PCT and WBC counts. In the prospective study, the levels of suPAR and sCD14-ST in both the Intra-bac BSIs and the Extra-bac BSIs groups were significantly higher than those in the viral infection group and normal control group (P < 0.05). The areas under the curve (AUC) of Intra-bac BSIs were 0.830 for suPAR, and 0.855 for sCD14-ST. The sensitivity, specificity, Youden's index for suPAR and sCD14-ST were respectively 76.5%, 88.2%, 0.647 and 94.1%, 64.7%, 0.588. Our multi-center study demonstrated that while the traditional inflammatory markers such as PCT, WBC counts, NEU% could not be served as promising diagnostic markers for Intra-bac BSIs; CRP can help guide the diagnosis of Intra-bac BSIs; Both suPAR and sCD14-ST could be considered as novel diagnostic biomarkers for Intra-bac BSIs as they showed good diagnostic accuracies in Intra-bac BSIs, especially suPAR.