Abstract: OBJECTIVE To explore the values of procalcitonin (PCT) in the identification and classification of Escherichia coli and ESBLs-producing E. coli, Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) in bloodstream infections. METHODS A total of 5646 blood culture specimens who were admitted to Wuhan Central Hospital from Jan. 2015 to Dec. 2015 were retrospectively analyzed, and 1658 cases were selected, including 1426 cases in negative group and 232 cases in positive group. Among the 178 blood culture in the positive group which had eliminated pollution, 96 were detected as gram-negative bacteria and 82 were gram-positive bacteria. The level of PCT was detected by automatic electrochemical luminescence instrument. Blood culture was conducted by an automatic bacteria mycobacterium cultivation monitoring system and the bacterial culture and identification were carried out by an automatic microbe identifying system. RESULTS The sensitivity and specificity of ROC curve of PCT for detecting positive and negative blood culture were 78.40% and 62.00% respectively. The level of PCT in negative group was (37.42±13.55)ng/ml, which was significantly higher than (11.22±3.56)ng/ml in positive group (P<0.05). When the level of PCT > 10.0 ng/ml, the quantity of gram-negative bacteria was significantly higher than that of gram positive bacteria (P<0.05). Meanwhile, the average PCT level of ESBLs-producing E. coli was significantly higher than that of E. coli, and the average PCT level of MRSA was significantly lower than that of S. aureus (P<0.05). CONCLUSION By detecting the concentration of PCT, gram-positive bacteria can be quickly distinguished from gram-negative bacteria in bloodstream infections. When the level of PCT > 10 ng/ml, the possibility of gram-negative bacteria infection is extremely high. Moreover, the PCT level of the patients with ESBLs-producing E. coli was higher than that of the patients with E. coli. The PCT level of the patients with MRSA was lover than that of the patients with S. aureus.