title: Procalcitonin levels in febrile infants after recent immunization.
abstract: BACKGROUND
  Procalcitonin has been identified as a useful blood marker of serious bacterial infection in febrile infants. Many infants present with a febrile reaction after receiving immunizations. The effects of immunization on procalcitonin have not been investigated.
  
  
  METHODS
  We performed a prospective observational cohort study at a large, urban pediatric emergency department. Infants <or=90 days of age with fever of >or=38 degrees C were enrolled. Subjects were divided into 3 groups: infants with serious bacterial infection; subjects without serious bacterial infection who received recent (<48 hours) immunizations; and subjects without serious bacterial infection who did not recently receive immunizations. Procalcitonin was measured by using a quantitative immunometric assay.
  
  
  RESULTS
  Over 13 months, procalcitonin was measured for 271 infants. There were 44 (16%) patients with serious bacterial infection, 35 in the recent-immunization group, and 192 in the no-recent-immunization group. The median procalcitonin level for serious bacterial infection was 0.53 ng/mL, for recent immunization was 0.29 ng/mL, and for no recent immunizations was 0.17 ng/mL. Procalcitonin values were elevated for patients with serious bacterial infection compared with patients both with and without recent immunizations. Compared with patients who had no recent immunizations, procalcitonin levels were elevated in patients with recent immunization. Using a cut point of 0.12 ng/mL, the sensitivity of procalcitonin for serious bacterial infection was 96%, specificity was 23%, and negative predictive value was 96%. Two patients with recent immunization who had serious bacterial infection were identified with this cut point.
  
  
  CONCLUSIONS
  Among febrile infants with recent immunization, procalcitonin levels are increased compared with patients with fever and no identified bacterial infection. Despite this increase, procalcitonin can still reliably discriminate infants with serious bacterial infection.
authors.affiliation: Divisions of Endocrinology, Children's Hospital Boston, Boston, Massachusetts 02115, USA. andrew.dauber@childrens.harvard.edu
authors.forename: Andrew
authors.initials: A
authors.lastname: Dauber
authors.forename: Scott
authors.initials: S
authors.lastname: Weiss
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Maniaci
authors.forename: Eric
authors.initials: E
authors.lastname: Nylen
authors.forename: Kenneth L
authors.initials: KL
authors.lastname: Becker
authors.forename: Richard
authors.initials: R
authors.lastname: Bachur
mesh_terms: D001424:Bacterial Infections / Q000097:blood*; D015415:Biomarkers / Q000097:blood; D002116:Calcitonin / Q000097:blood*; D015740:Calcitonin Gene-Related Peptide; D005260:Female; D005334:Fever / Q000097:blood*; D006801:Humans; D007114:Immunization; D007223:Infant; D007231:Infant, Newborn; D007958:Leukocyte Count; D008297:Male; D011446:Prospective Studies; D011498:Protein Precursors / Q000097:blood*; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers; C000606589:CALCA protein, human; D011498:Protein Precursors; D002116:Calcitonin; D015740:Calcitonin Gene-Related Peptide