Predictive value of procalcitonin for excluding bloodstream infection: results of a retrospective study and utility of a rapid, quantitative test for procalcitonin.

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.