Keywords: 
• bloodstream infection /
• blood culture /
• procalcitonin /
• antibacterias

Abstract: Objective To investigate the relationship between procalcitonin (PCT) levels and bacteria in patients with bloodstream infection who were already administered antimicrobial therapy. Methods Retrospective collected the patients with monomicrobial bloodstream infection who were already administered antimicrobial therapy in First Hospital Affiliated to Soochow University from Sept. 2011 to Dec. 2016. Blood samples for PCT testing and culture were collected at the same time. Correlational analysis of PCT levels and bacteria was performed. Results 119 patients were in accordance with the inclusive criteria. 37 patients(31.1%)were infected with gram-positive(G⁺) bacteria and 82 patients(68.9%)were infected with gram-negative(G^-) bacteria.The median (interquartile range, IQR) of PCT were 0.49 (0.16-1.59) ng/ml and 0.71 (0.27-2.74) ng/ml for G⁺ and G^- infection, respectively (P=0.109). Enterococcus and enterobacter had the highest PCT levels among G⁺ and G^- bacteria, the median (IQR) of PCT were 3.35(0.95-28.79) ng/ml and 5.25 (0.22-35.89) ng/ml, respectively. PCT levels in different cohorts existed significant differences (P=0.001). Conclusion For patients with bloodstream infection who were already administered antimicrobial therapy, PCT levels were unable to distinguish G^- from G⁺ bacteria.