'Modest at best' discriminatory ability for CBC test in infants

(HealthDay)—Complete blood cell count parameters at commonly used or optimal thresholds do not offer high accuracy in identifying invasive bacterial infections (IBIs) in febrile infants (≤60 days of age), according to a study published online Sept. 11 in JAMA Pediatrics.

Andrea T. Cruz, M.D., from the Baylor College of Medicine in Houston, and colleagues conducted planned secondary analysis of a prospective observational cohort study that included 4,313 febrile (≥38 C), previously healthy, full-term infants (≤60 days) from 26 emergency departments in the Pediatric Emergency Care Applied Research Network (from 2008 to 2013). The accuracies of the white blood cell count, absolute neutrophil count, and platelet count were assessed for detecting IBIs.

The researchers found that 2.2 percent had IBIs. Sensitivities were low for common complete blood cell count thresholds: white blood cell count <5,000/µL, 10 percent; white blood cell count ≥15,000/µL, 27 percent; absolute neutrophil count ≥10,000/µL, 18 percent; and platelets <100 × 10³/µL, 7 percent. Optimal thresholds (with corresponding areas under the receiver operating characteristic) for white blood cell count were 11,600/µL (0.57), absolute neutrophil count of 4,100/µL (0.70), and platelet count of 362 × 103/µL (0.61).

"Physicians who use CBC thresholds in an attempt to risk stratify febrile young infants may be falsely reassured by normal CBC parameters. When used in isolation, either at commonly used thresholds or at the optimal thresholds identified here, CBC parameters have at best modest discriminatory ability," the authors write. "In an era where better screening tests exist to identify infants with IBIs, we need to question our continual reliance on a test whose greatest strength may simply be in its ready availability in clinical practice."

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