Objective Sepsis is one of the leading causes of mortality in critically ill patients, and providing a timely diagnosis and early intervention is necessary for successful treatment. Procalcitonin (PCT) may be a better marker of sepsis than conventional inflammatory markers. The aim of this study was to evaluate the clinical utility of the PCT level as a marker of sepsis. Methods Forty-five patients with sepsis, 24 patients with pneumonia who did not meet the SIRS criteria (PN) and 56 controls were enrolled in this study. The levels of PCT and other serum markers were measured, and their utility as markers of sepsis was assessed. Results The serum PCT levels exhibited statistically significant differences between the three groups (p< 0.0001). The PCT levels in the sepsis group (29.3±85.3 ng/mL) were significantly higher (p<0.001) than those observed in the PN group (0.34±8.6 ng/mL) and the control group (0.74±2.1 ng/mL), according to a post hoc analysis. There were no differences in the white blood cell (WBC) counts or C-reactive protein (CRP) levels between the three groups. Fourteen of the 45 patients with sepsis had positive microbiological blood cultures (Gram-positive cocci [GPC] in seven patients, Gram-negative rods [GNR] in six patients, other types of bacteria in one patient). The 13 patients with GNR or GPC were categorized into the GNR group or GPC group according to the identified pathogens. The serum PCT levels were significantly higher in the GNR group (149.8±199.7 ng/mL) than in the GPC group (19.1±41.8 ng/mL) (p<0.05), although there were no differences in the WBC counts or CRP levels between these groups. When the cut-off value for the PCT level was set at 16.9 ng/mL, the sensitivity and specificity for the detection of GNR infection were 85.7% and 83.3%, respectively. Conclusion The PCT level is a potentially useful marker of the type of causative pathogen in patients with sepsis whose measurement may facilitate the selection of appropriate empiric antibiotic treatment.

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The Authors Reply We appreciate the interest and comments from Dr. Mustafa Hatipoglu et al. regarding our study (1). Their major concern is that Staphylococcus aureus (S. aureus) was not included in the Gram-positive cocci group for the comparison of the procalcitonin (PCT) levels between the patients with sepsis caused by Gram-positive cocci and that caused by Gram-negative rods.When we performed the prospective study (between May and December 2010), patients with sepsis caused by S. aureus were not included by chance. Therefore, we did not have an opportunity to evaluate the PCT levels in patients with sepsis caused by S. aureus. This time, we retrospectively observed an association between the PCT level and sepsis caused by S. aureus by reviewing the subjects' medical records. Seventeen patients with sepsis caused by S. aureus were admitted to our hospital between January and December 2013. The mean PCT level for these patients was 2.9±3.4 ng/mL, with a maximum of 11.2 ng/mL. These PCT levels were lower than those of the patients with sepsis caused by Gram-negative rods included in the study (149.8± 199.7 ng/mL) (1). Furthermore, the PCT level in each patient with sepsis caused by S. aureus was less than 16.9 ng/ mL, the estimated cut-off level for predicting causative pathogen type in our study (1). Hence, considering the data obtained from our retrospective observation, the PCT levels in the patients with sepsis caused by S. aureus were not as high as those observed in the patients with sepsis caused by Gram-negative rods.On the other hand, Dr. Mustafa Hatipoglu et al. pointed to a recent study reporting that the PCT levels of patients with S. aureus bacteremia (median: 0.85 ng/mL) are as high as those of patients with bacteremia resulting from Gramnegative rods (median: 0.78 ng/mL) (2). The patients recruited in that study appear to have had bacteremia without sepsis; clear criteria for sepsis or systemic inflammatory response syndrome (SIRS) were not used for inclusion in that study.Collectively, we believe that the PCT level is a potential marker of the type of causative pathogen in patients with sepsis. On the other hand, as we mentioned in the discussion section of our study (1), our analysis was limited by the number of recruited patients. The PCT level is known to be affected by various factors; therefore, we are planning a larger study to confirm our results and the diagnostic potential of PCT measurements. The authors state that they have no Conflict of Interest (COI).