title: Diagnostic markers of infection: comparison of procalcitonin with C reactive protein and leucocyte count.
abstract: BACKGROUND
  Procalcitonin has been advocated as a marker of bacterial infection.
  
  
  OBJECTIVE
  To evaluate diagnostic markers of infection in critically ill children, comparing procalcitonin with C reactive protein and leucocyte count in a paediatric intensive care unit (PICU).
  
  
  METHODS
  Procalcitonin, C reactive protein, and leucocyte count were measured in 175 children, median age 16 months, on admission to the PICU. Patients were classified as: non-infected controls (43); viral infection (14); localised bacterial infection without shock (25); bacterial meningitis/encephalitis (10); or septic shock (77). Six children with "presumed septic shock" (without sufficient evidence of infection) were analysed separately. Optimum sensitivity, specificity, predictive values, and area under the receiver operating characteristic (ROC) curve were evaluated.
  
  
  RESULTS
  Admission procalcitonin was significantly higher in children with septic shock (median 94.6; range 3.3-759.8 ng/ml), compared with localised bacterial 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 meningitis had a median procalcitonin of 25.5 (7.2-118.4 ng/ml). Area under the ROC 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 septic shock were: procalcitonin > 20 ng/ml and C reactive protein > 50 mg/litre. A procalcitonin concentration > 2 ng/ml identified all patients with bacterial meningitis or septic shock.
  
  
  CONCLUSIONS
  In critically ill children the admission procalcitonin concentration is a better diagnostic marker of infection than C reactive protein or leucocyte count. A procalcitonin concentration of 2 ng/ml might be useful in differentiating severe bacterial disease in infants and children.
authors.affiliation: Paediatric Intensive Care Unit, Guy's Hospital, St Thomas's Street, London SE1 9RT, UK.
authors.forename: M
authors.initials: M
authors.lastname: Hatherill
authors.forename: S M
authors.initials: SM
authors.lastname: Tibby
authors.forename: K
authors.initials: K
authors.lastname: Sykes
authors.forename: C
authors.initials: C
authors.lastname: Turner
authors.forename: I A
authors.initials: IA
authors.lastname: Murdoch
mesh_terms: D000293:Adolescent; D000367:Age Factors; D000704:Analysis of Variance; D001424:Bacterial Infections / Q000097:blood / Q000175:diagnosis*; D015415:Biomarkers / Q000097:blood; D002097:C-Reactive Protein / Q000032:analysis*; D002116:Calcitonin / Q000097:blood*; D015740:Calcitonin Gene-Related Peptide; D002648:Child; D002675:Child, Preschool; D003422:Critical Care / Q000379:methods; D006023:Glycoproteins / Q000097:blood*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D007958:Leukocyte Count; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011498:Protein Precursors / Q000097:blood*; D012372:ROC Curve; D012772:Shock, Septic / Q000175:diagnosis / Q000382:microbiology
chemical_list: D015415:Biomarkers; C000606589:CALCA protein, human; D006023:Glycoproteins; D011498:Protein Precursors; D002116:Calcitonin; D002097:C-Reactive Protein; D015740:Calcitonin Gene-Related Peptide