title: Reactive thrombocytosis in febrile young infants with serious bacterial infection.
abstract: OBJECTIVE
  to estimate the incidence of reactive thrombocytosis among febrile young infants and to asses the utility of platelet count as a potential predictor of serious bacterial infection (SBI).
  
  
  METHODS
  retrospective study between January 2005 and December 2008.
  
  
  METHODS
  tertiary care pediatric unit.
  
  
  METHODS
  all infants 29 to 89 days of age, admitted with rectal temperature > 38oC without a focus of infection.
  
  
  METHODS
  the results of the sepsis evaluation on admission were recorded. SBI included all cases of occult bacteremia, urinary tract infection, bacterial meningitis, pneumonia, bacterial gastroenteritis and infections of the soft tissues and bones.
  
  
  RESULTS
  of the 408 infants studied, 103 (25.2%) had SBI. Platelet count was significantly higher in infants with SBI compared to those without (median 513000 /mm3 [interquartile range 455,000-598,000/mm3] vs median 398000/mm3; [interquartile range 313,000-463,000/mm3]; P<0.001). Thrombocytosis had only moderate ability in predicting SBI (area under the curve: 0.74, 95 % CI 0.70-0.79). The combination of platelet count >450,000/mm3, WBC >15,000/mm3, Creactive protein >2 mg/dL, and pyuria >10 WBC/hpf would lead to misclassification of 4 infants with SBI (3.9% of SBIs; negative likelihood ratio 0.08).
  
  
  CONCLUSIONS
  reactive thrombocytosis was a frequent finding in young infants with SBI. Thrombocytosis >450,000 cells/mm3, in combination with leucocytosis, elevated CRP and pyuria, may help in early recognition of febrile young infants at risk for SBI.
authors.affiliation: Department of Pediatrics, University Hospital of Patras, Patras, Greece. sfouzas@gmail.com
authors.forename: S
authors.initials: S
authors.lastname: Fouzas
authors.forename: L
authors.initials: L
authors.lastname: Mantagou
authors.forename: E
authors.initials: E
authors.lastname: Skylogianni
authors.forename: A
authors.initials: A
authors.lastname: Varvarigou
mesh_terms: D001424:Bacterial Infections / Q000097:blood*; D005260:Female; D005334:Fever / Q000097:blood / Q000382:microbiology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D012189:Retrospective Studies; D013922:Thrombocytosis / Q000382:microbiology*