Abstract: OBJECTIVE To explore the clinical value of serum procalcitonin (PCT) in identification of pathogens causing bloodstream infections and judgment of the bloodstream infections.METHODS From Aug 2014 to Aug 2016, totally 126 patients who were clinically diagnosed with bloodstream infections were enrolled in the study, then the blood specimens that were collected from the patients with infections were cultured, the patients were divided into the gram-positive bacteria group with 60 cases and the gram-negative bacteria group with 66 cases, the constituent ratios of the species of pathogens isolated from the two groups of patients were studied, the serum PCT concentration was determined and compared with the result of positive pathological diagnosis, the association between the serum PCT concentration and the pathogens causing the bloodstream infections was analyzed, and the effect of serum PCT on differential identification of the pathogens causing the bloodstream infections was observed.RESULTS A total of 60 strains of gram-positive bacteria were isolated from the 126 patients with bloodstream infections, accounting for 47.6%, Streptococcus pyogenes, Staphylococcus aureus, and Enterococcus spp were dominant among the gram-positive bacteria.The gram-negative bacteria accounted for 52.4% (66 strains), among which Escherichia coli, Acinetobacter baumannii, and Klebsiella pneumoniae were dominant.The median serum PCT concentration of the gram-positive bacteria group was 2.13 ng/ml, with the serum PCT concentration ranging between 0.31 and 5.87 ng/ml; the median serum PCT concentration of the gram-negative bacteria was 9.38 ng/ml, with the serum PCT concentration ranging between 6.91 and 11.73 ng/ml; there was significant difference in the median serum PCT concentration or the range of serum PCT concentration between the two groups of patients (P＜0.05).Among the gram-positive bacteria, the PCT concentration of S.aureus was 5.87 ng/ml, the PCT concentration of Enterococcus spp 0.78 ng/ml, the PCT concentration of S.pyogenes 0.31 ng/ml, and there was significant difference in the PCT concentration between S.aureus and Enterococcus spp, between S.aureus and S.pyogenes, or between Enterococcus spp and S.pyogenes (P＜0.05).Among the gram-negative bacteria, the PCT concentration of E.coli was 11.73 ng/ml, the PCT concentration of A.baumannii 7.39 ng/ml, the PCT concentration of K.pneumoniae 6.91 ng/ml, and there was significant difference in the PCT concentration between E.coli and A.baumannii, E.coli and K.pneumoniae, or between A.baumannii and K.pneumoniae (P＜0.05). Compared with the PCT concentration detection of the gram-positive bacteria and the result of positive pathological diagnosis, it was suggested that the positive prediction rate of diagnosis of the gram-positive bacteria bloodstream infection reached 78.3%; Compared with the PCT concentration detection of the gram-negative bacteria and the result of positive pathological diagnosis, it was concluded that the positive prediction rate of diagnosis of the gram-negative bacteria bloodstream infection was as high as 90.9%.CONCLUSIONThe serum PCT may achieve remarkable effect on judgment of the patients with bloodstream infections and plays a supporting role in identification of the gram-negative bacteria and the gram-positive bacteria, which has high reference value in assessment of types of the bloodstream infections and selection of treatment programs.