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In May 1996, the CDC recommended obtaining a complete blood count and blood culture (BC) from all asymptomatic “at risk” newborns; those ≥35 weeks gestation born to mothers with group B streptococcal vaginal colonization or those with maternal fever, premature rupture of membranes or previous infant with group B streptococcal disease; who did not receive adequate intrapartum antibiotic prophylaxis.During the study period (May 1996 to July 1999), a complete blood count and BC were obtained within 4 h from all asymptomatic at risk newborns of ≥35 weeks gestation. White blood cell count (WBC) and BC results and prevalence of clinical or culture-proven sepsis were obtained by chart review. We determined the sensitivity/specificity and likelihood ratios of an abnormal WBC (total >30 000 or <5000/mm3; absolute neutrophil count <1500/mm3, or a band form-polymorphonuclear cell ratio of >0.2) to distinguish between clinically septic vs. nonseptic term at risk newborns.Of 20 554 deliveries 1665 were initially asymptomatic at risk newborns; 17 (1.0%) developed early onset sepsis, all within 48 h. WBC was abnormal in 7 of 17 (41%) and in 447 of 1648 (27%) who remained nonseptic. None of the 1665 term at risk newborns had a positive BC. The sensitivity and specificity of an abnormal WBC in predicting which at risk newborns would develop sepsis were 41 and 73%, respectively. The positive likelihood ratio was 1.52, whereas the negative likelihood ratio was 0.81, with an odds ratio of 1.88.Since the implementation of the CDC guidelines for maternal intrapartum antibiotic prophylaxis, culture-proved sepsis has become rare at our institution. Although BC did not aid in the diagnosis of sepsis among asymptomatic at risk newborns, close observation in the first 24 h remained critically important.