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Objectives: To assess retrospectively the diagnostic value of procalcitonin (PCT) in excluding suspected bloodstream infection, establish cut-off values for PCT levels, and compare PCT with other clinical markers., Methods: The predictive accuracy of different continuous parameters was estimated by univariate analysis of the area under the receiver operating characteristic curve. Optimized cut-off points for the parameters were selected according to the maximum Youden index values, which in turn were used to define positive and negative predictive values of different parameters in diagnosing bloodstream infection., Results: The PCT level yielded a statistically significant area under the receiver operating characteristic curve of 0.765, with a best cut-off value of 0.80 ng/ml (83% sensitivity; 65% specificity, Youden index, J = 0.48). Positive and negative predictive values at this cut-off value were 38% and 94%, respectively. Mann-Whitney U-test revealed significantly higher values for PCT, C-reactive protein and percentage of neutrophils, but not for white blood cell count, in patients with bloodstream infection., Conclusions: The serum PCT level can potentially be used as surrogate marker to exclude bacteraemia and to inform critical management decisions regarding antibiotic usage, in patients admitted with suspected bloodstream infection.

A set of real-time PCR based assays using the locked nucleic acid probes from Roche Universal ProbeLibrary were developed for rapid detection of eight bacterial species from positive blood culture bottles. Four duplex real-time PCR reactions targeting to one Gram-positive bacterium and one Gram-negative bacterium were optimized for species identification according to Gram stain results. We also included mecA-specific primers and probes in the assays to indicate the presence of methicillin resistance in the bacterial species. The analytical sensitivity was in the range of 1-10 CFU per PCR reaction mixture. The specificity and cross reactivity of the assay was validated by 28 ATCC reference strains and 77 negative blood culture specimens. No cross-reactivity was observed in these samples thus demonstrating 100 % specificity. 72 previously characterized clinical isolates were tested by the real-time PCR assay and validated the accuracy and feasibility of the real-time PCR assay. Furthermore, 55 positive blood culture samples were tested using real-time PCR and 50 (90.9 %) of them were identified as the same species as judged by biochemical analysis. In total, real-time PCR showed 98.2 % consistent to that of traditional methods. Real-time PCR can be used as a supplement for early detection of the frequently-occurred pathogens from the positive blood cultures. [ABSTRACT FROM AUTHOR]