Procalcitonin in the assessment of bacteraemia in emergency department patients: results of a large retrospective study

Background: The aim of this study was to evaluate the use of procalcitonin in the assessment of bacteraemia in patients in the emergency department, both alone and in conjunction with existing inflammatory markers of bacterial infection. Methods: We enrolled 3305 cases (range 20–90 years) for which we retrospectively compared procalcitonin concentration, blood culture results, body temperature, absolute neutrophil count, and C-reactive protein concentration. The positive predictive value and the negative predictive value of procalcitonin were established at different cut-off concentrations. Receiver operating characteristic curves were plotted, and the areas under the ROC curves calculated, to allow assessment of the diagnostic accuracy of (a) a combination of three existing inflammatory markers of bacterial infection (body temperature, C-reactive protein, absolute neutrophil count), and (b) this combination with procalcitonin. Results: Positive predictive values of procalcitonin using 0.1, 1, 2, and 5 ng/mL as the cut-off values were 21.2, 32.2, 34.2, and 37.0%, respectively. Negative predictive values of procalcitonin using 0.1, 1, 2, and 5 ng/mL as the cut-off values were 95.1, 92.2, 91.1, and 89.0%, respectively. Areas under the curve of three inflammatory markers (absolute neutrophil count, C-reactive protein, and body temperature) combined was 0.879; areas under the curve of these markers combined with procalcitonin was 0.932 (p = 0.018). Conclusions: When procalcitonin is used as a serum marker for ruling out bacteraemia, a cut-off of 0.1 ng/mL may be used. Procalcitonin improves the diagnostic accuracy of existing markers of bacteraemia.