Use of the complete blood cell count in late-onset neonatal sepsis

Abstract

Background: Late-onset sepsis is an important cause of morbidity and mortality in infants. Diagnosis of late-onset sepsis can be challenging. The complete blood cell count and differential have been previously evaluated as diagnostic tools for late-onset sepsis in small, single-center reports.

Objective: We evaluated the diagnostic accuracy of the complete blood cell count and differential in late-onset sepsis in a large multicenter population.

Study design: Using a cohort of all infants with cultures and complete blood cell count data from a large administrative database, we calculated odds ratios for infection, as well as sensitivity, specificity, positive and negative predictive values and likelihood ratios for various commonly used cut-off values.

Results: High and low white blood cell counts, high absolute neutrophil counts, high immature-to-total neutrophil ratios and low platelet counts were associated with late-onset sepsis. Associations were weaker with increasing postnatal age at the time of the culture. Specificity was highest for white blood cell counts <1000/mm and >50,000/mm (>99%). Positive likelihood ratios were highest for white blood cell counts <1000/mm (4.1) and platelet counts <50,000/mm (3.5).

Conclusion: No complete blood cell count index possessed adequate sensitivity to reliably rule out late-onset sepsis in this population.

FIGURE 1

Association between complete blood cell count indices and late-onset sepsis (>72 hours). A. WBC vintiles and ORs; B. ANC vintiles and ORs; C. I/T ratio vintiles and ORs; D. Platelet vintiles and ORs. WBC indicates white blood cell; ANC, absolute neutrophil count; I/T ratio, immature-to-total neutrophil ratio; OR, odds ratio.

FIGURE 2

Receiver operating characteristic (ROC) curves for complete blood cell count indices. A. I/T ratio (AUC=0.606); B. Platelet count (AUC=0.606); C. WBC count <15,000/mm³ (AUC=0.550); D. ANC (AUC=0.534); E. WBC count >15,000/mm³ (AUC=0.525). WBC indicates white blood cell; ANC, absolute neutrophil count; I/T ratio, immature-to-total neutrophil ratio; AUC, area under the curve.