Circulating neutrophils in septic preterm neonates: comparison of two reference ranges

To study the effect of sepsis on circulating neutrophils in very low birth weight neonates and to assess the usefulness of recently revised reference ranges for circulating neutrophils in the diagnosis of sepsis in this population by comparison with previously reported reference ranges.

Neutrophil parameters (absolute total neutrophils, absolute total immature neutrophils, and the immature:total neutrophil proportion) were analyzed retrospectively in 202 sepsis episodes in 192 neonates (birth weight = 1055 +/- 246 g, X +/- SD; estimated gestational age = 29 +/- 2 weeks) between birth and 30 days of age. The percentage of values lying outside the reference ranges reported recently by Mouzinho et al and previously by Manroe et al were compared. To more accurately assess possible differences in specificity between the two reference ranges, neonates with early-onset group B streptococcal infection (n = 19) were compared with a matched control group (n = 51) using conditional logistic regression.

Greater sensitivity was observed using the previous reference ranges of Manroe et al over the entire study period (0 to 720 hours) both for the initial and the second complete blood count (CBC). The previous reference ranges also were more sensitive than the revised ranges for the initial CBC at 0 to 72 and at 73 to 720 hours and for infections attributable to coagulase-negative staphylococci. However, specificity in neonates without group B streptococcal infection was significantly greater with the revised reference ranges compared with those of Manroe et al (initial CBC, 73% vs 45%; serial CBCs, 59% vs 10%).

The observed differences in sensitivities may be of limited clinical significance because very low birth weight infants often are begun on antibiotic therapy regardless of laboratory values. However, the striking differences in specificity using the revised reference ranges suggest that these ranges may be clinically useful in determining length of antimicrobial therapy in infants in whom cultures remain sterile.