Are Complete Blood Cell Counts Useful in the Evaluation of Asymptomatic Neonates Exposed to Suspected Chorioamnionitis?

Abstract

Reportedly, chorioamnionitis complicates as many as 10% of pregnancies, and the condition poses a risk of neonatal infection. Affected women receive antibiotics, which may render neonatal blood cultures inconclusive. This prospective observational study was done to establish whether peripheral neutrophil counts might aid the diagnosis of neonatal infection and help decide the duration of antibiotic treatment. Participants were 856 near-term or term infants whose mothers were suspected of having chorioamnionitis. The infants received antibiotics for 48 hours unless clinical infection was present or a blood culture was positive. A blood culture was done and complete blood cell count (CBC) obtained within an hour of birth, and counts were repeated at approximately 12 and 24 hours. The results were analyzed using 2 reference systems, the ranges of Manroe et al. and the normal ranges of Schjelonka et al. Half the asymptomatic infants were followed up after discharge to identify recurrent infection. All but 4% of newborn infants were asymptomatic and had negative cultures. Antibiotics were discontinued at 48 hours in these cases. At least 1 abnormal neutrophil count was found in 99% of asymptomatic infants. Of infants having all 3 planned complete blood counts, 97% of those with symptoms had 1 or more abnormal neutrophil counts. Four infants (0.5%) had positive blood cultures, but 3 were asymptomatic. Eight of 404 asymptomatic infants who were followed up required rehospitalization within 3 weeks of discharge, 4 of them because of fever with a negative workup for sepsis and antibiotic treatment for less than 3 days. No infant had evidence of bacterial infection. The specificity and negative predictive values for abnormal neutrophil counts ranged from 0.12 to 0.95 and from 0.91 to 0.97, respectively. The range of sensitivity was 0.27 to 0.76. Initial neutrophil counts differed depending on which reference values were used. Had neutrophil counts been used to determine the duration of antibiotic therapy in this population, local costs would have risen by $76,000 to $425,000 per year. Neither single nor serial neutrophil counts aid the diagnosis of early-onset infection, and they are not a helpful guide to the duration of antibiotic treatment in asymptomatic infants with negative cultures whose mothers are suspected of having chorioamnionitis.