Diagnostic markers of infection: comparison of procalcitonin with C reactive protein and leucocyte count

Background-Procalcitonin has been advocated as a marker of bacterial infect ion. Objective-To evaluate diagnostic markers of infection in critically ill chi ldren, comparing procalcitonin with C reactive protein and leucocyte count in a paediartric intensive care unit (PICU). Methods-Procalcitonin, C reactive protein, and leucocyte count were measure d in 175 children, median age lei months, on admission to the PICU. Patient s were classified as: non-infected controls (43); viral infection (14); loc alised bacterial infection without shock (25); bacterial meningitis/encepha litis (10); or septic shock (77). Six children with "presumed septic shock" (without sufficient evidence of infection) were analysed separately; Optim um sensitivity, specificity, predictive values, and area under the receiver operating characteristic (ROC) curve were evaluated. Results-Admission procalcitonin was significantly higher in children with s eptic shock (median 94.6; range 3.3-759.8 ng/ml), compared with localised b acterial infection (2.9; 0-24.3 ng/ml), viral infection (0.8; 0-4.4 ng/ml), and non-infected controls (0; 0-4.9 ng/ml). Children with bacterial mening itis had a median procalcitonin of 25.5 (7.2-118.4 ng/ml). Area under the R OC curve was 0.96 for procalcitonin, 0.83 for C reactive protein, and 0.51 for leucocyte count. Cut off concentrations for optimum prediction of septi c shock were: procalcitonin > 20 ng/ml and C reactive protein > 50 mg/litre . A procalcitonin concentration > 2 ng/ml identified all patients with bact erial meningitis or septic shock. Conclusion-In critically ill children the admission procalcitonin concentra tion is a better diagnostic marker of infection than C reactive protein or leucocyte count. A procalcitonin concentration of 2 ng/ml might be useful i n differentiating severe bacterial disease in infants and children.