Background: Bacteremia is a life-threatening infection, and prognosis is highly dependent on early recognition and treatment with appropriate antimicrobial agents. We investigated the diagnostic performance of serum procalcitonin (PCT) for differentiation between contaminants and true pathogens in blood cultures. 

Methods: Serum PCT, C-reactive protein (CRP) and blood culture were performed for 473 patients between February 2008 and October 2008. We retrospectively reviewed the patients’ clinical characteristics and laboratory results based on medical records. 

Results: The mean concentration of PCT was significantly different between the two negative and positive blood culture groups (6.45 ng/mL vs 28.77 ng/ mL, P＜0.001). Procalcitonin levels were found to be markedly higher in those with Gram-negative bacilli (mean±SD; 59.58±67.00 ng/mL) bacteremia than in those with Gram-positive cocci (mean±SD; 17.75±42.88 ng/mL) bacteremia (P＜0.001). The areas under the receiver operating characteristic curves (95% confidence interval) for PCT and CRP were 0.880 (0.820∼ 0.940) and 0.637 (0.538∼0.736), respectively. The use of a PCT level of 2 ng/mL as a cutoff value yielded an 83.6% positive predictive value and a 77.4% negative predictive value for the detection of bacteremia pathogens. 

Conclusion: Serum PCT is a helpful diagnostic marker for rapidly and accurately distinguishing between contaminants and pathogens in blood cultures. (Korean J Clin Microbiol 2011;14:7-12)