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?
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%).
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.
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.
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.
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.
Cruz AT, Mahajan P, Bonsu BK, Bennett JE, Levine DA, Alpern ER, Nigrovic LE, Atabaki SM, Cohen DM, VanBuren JM, Ramilo O, Kuppermann N, for the Febrile Infant Working Group of the Pediatric Emergency Care Applied Research Network. Accuracy of Complete Blood Cell Counts to Identify Febrile Infants 60 Days or Younger With Invasive Bacterial Infections. JAMA Pediatr. Published online September 11, 2017. doi:10.1001/jamapediatrics.2017.2927