Background Septic shock caused by bacteremia is a life-threatening infection whose prognosis is highly dependent on early recognition and appropriate treatment.Procalcitonin (PCT) has been shown to accurately and quickly distinguish bacteremia from noninfectious inflammatory states in critically severe patients.However,the extent of PCT magnitude elevation according to the Gram stain result in elderly patients with coronary heart disease (CHD) at the onset of septic shock caused by bacteremia varies,and has not been clearly elucidated.Methods The medical records of advanced age (non-neutropenic) patient with CHD and septic shock between Mar 2013 and Jun 2015 who had bacteremia caused by either Gram-positive (GP) bacteria or Gram-negative (GN) bacteria were reviewed,and the levels of PCT,C-reactive (CRP) protein and white blood cells count (WBC) in both groups were analyzed.Results 75 episodes of either GN bacteremia (n =40) or GP bacteremia (n =35) were enrolled.PCT levels were found to be markedly higher in patients with GN bacteremia than in those with GP bacteremia [(8.93 ± 17.58) vs.(64.42 ± 58.56) ng/L (P ＜ 0.001)],whereas there was no significant difference in CRP and WBC (P ＞ 0.05).Moreover,a high PCT level was found to be independently associated with GN bacteremia in this study population.A PCT level of 19.69 ng/mL yielded a 72.5％ sensitivity,a 91.4％ specificity,an 8.43 positive likelihood ratio and a 0.30 negative likelihood ratio for GN-related bacteremia in the study cohort [AUROCC =0.870 (0.041),95％ CI (0.790-0.949)].Conclusion In an elderly patient (non-neutropenic)with CHD and septic shock,GN bacteremia could be associated with higher PCT values than those found in GP bacteremia (PCT ＞ 19.69 ng/mL).