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Original Investigation
September 11, 2017

Accuracy of Complete Blood Cell Counts to Identify Febrile Infants 60 Days or Younger With Invasive Bacterial Infections

Author Affiliations
  • 1Sections of Pediatric Emergency Medicine and Pediatric Infectious Diseases, Baylor College of Medicine, Houston, Texas
  • 2Departments of Emergency Medicine and Pediatrics, University of Michigan, Ann Arbor
  • 3Division of Emergency Medicine, Department of Pediatrics, Nationwide Children’s Hospital and The Ohio State University, Columbus
  • 4Division of Pediatric Emergency Medicine, Alfred I. DuPont Hospital for Children, Nemours Children’s Health System, Wilmington, Delaware
  • 5Department of Emergency Medicine and Pediatrics, New York University Langone Medical Center, Bellevue Hospital Center, New York, New York
  • 6Ann and Robert H. Lurie Children’s Hospital of Chicago, Northwestern University Feinberg School of Medicine, Chicago, Illinois
  • 7Division of Emergency Medicine, Boston Children’s Hospital, Harvard Medical School, Boston, Massachusetts
  • 8Division of Emergency Medicine, Department of Pediatrics, Children’s National Medical Center, Washington, DC
  • 9Department of Pediatrics, University of Utah, Salt Lake City
  • 10Division of Pediatric Infectious Diseases and Center for Vaccines and Immunity, Nationwide Children’s Hospital and The Ohio State University, Columbus
  • 11Departments of Emergency Medicine and Pediatrics, University of California, Davis Health, Sacramento
JAMA Pediatr. Published online September 11, 2017. doi:10.1001/jamapediatrics.2017.2927
Key Points

Question  What is the accuracy of complete blood count parameters at routinely used thresholds in identifying young febrile infants with bacteremia or bacterial meningitis in the pneumococcal conjugate vaccine era?

Findings  In this cohort of 4313 febrile infants aged 0 to 60 days, 97 (2.2%) had bacteremia or bacterial meningitis. Sensitivities were low for white blood cell counts less than 5000/µL (sensitivity, 10%; specificity, 91%), white blood cell count ≥15 000/µL (sensitivity, 27%; specificity, 87%), and absolute neutrophil count ≥15 000/µL (sensitivity, 18%; specificity, 96%).

Meaning  No complete blood cell count parameter at routinely used thresholds in isolation identified infants with bacteremia or bacterial meningitis with sufficient accuracy to substantially assist clinical decision making.

Abstract

Importance  Clinicians often risk stratify young febrile infants for invasive bacterial infections (IBIs), defined as bacteremia and/or bacterial meningitis, using complete blood cell count parameters.

Objective  To estimate the accuracy of individual complete blood cell count parameters to identify febrile infants with IBIs.

Design, Setting, and Participants  Planned secondary analysis of a prospective observational cohort study comprising 26 emergency departments in the Pediatric Emergency Care Applied Research Network from 2008 to 2013. We included febrile (≥38°C), previously healthy, full-term infants younger than 60 days for whom blood cultures were obtained. All infants had either cerebrospinal fluid cultures or 7-day follow-up.

Main Outcomes and Measures  We tested the accuracy of the white blood cell count, absolute neutrophil count, and platelet count at commonly used thresholds for IBIs. We determined optimal thresholds using receiver operating characteristic curves.

Results  Of 4313 enrolled infants, 1340 (31%; 95% CI, 30% to 32%) were aged 0 to 28 days, 2412 were boys (56%), and 2471 were white (57%). Ninety-seven (2.2%; 95% CI, 1.8% to 2.7%) had IBIs. Sensitivities were low for common complete blood cell count parameter thresholds: white blood cell count less than 5000/µL, 10% (95% CI, 4% to 16%) (to convert to  × 109 per liter, multiply by 0.001); white blood cell count ≥15 000/µL, 27% (95% CI, 18% to 36%); absolute neutrophil count ≥10 000/µL, 18% (95% CI, 10% to 25%) (to convert to  × 109 per liter, multiply by 0.001); and platelets <100 x103 /µL, 7% (95% CI: 2% to 12%) (to convert to × 109 per liter, multiply by 1). Optimal thresholds for white blood cell count (11 600/µL), absolute neutrophil count (4100/µL), and platelet count (362 × 103/µL) were identified in models that had areas under the receiver operating characteristic curves of 0.57 (95% CI, 0.50-0.63), 0.70 (95% CI, 0.64-0.76), and 0.61 (95% CI, 0.55-0.67), respectively.

Conclusions and Relevance  No complete blood cell count parameter at commonly used or optimal thresholds identified febrile infants 60 days or younger with IBIs with high accuracy. Better diagnostic tools are needed to risk stratify young febrile infants for IBIs.

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