Serial measurements of C-reactive protein and interleukin-6 in the immediate postnatal period: Reference intervals and analysis of maternal and perinatal confounders

Background: There is a wide range of reported sensitivities and specificities for C-reactive protein (CRP) and interleukin-6 (IL-6) in the detection of early-onset neonatal infection. This prompted us to assess reference intervals for CRP and IL-6 during the 48-h period immediately after birth and to identify maternal and perinatal factors that may affect them. Methods: CRP and IL-6 values were prospectively obtained for 148 healthy babies (113 term, 35 near-term) at birth and at 24 and 48 h of life, and from their mothers at delivery. Results: Upper reference limits for CRP at each neonatal age were established. At birth, CRP was significantly lower than at 24 and 48 h of life. Rupture of membranes greater than or equal to 18 h, perinatal distress, and gestational hypertension significantly affected the neonatal CRP dynamics, but at specific ages. There was no correlation between CRP concentrations in mothers and their offspring at birth. The IL-6 values observed in the delivering mothers and in their babies at all three neonatal ages were negatively associated with gestational age. In the immediate postnatal period, IL-6 dynamics for term babies were significantly different from those for near-term babies. Maternal IL-6 concentrations correlated with babies' IL-6 concentrations only for term deliveries. Apgar score had a significant effect on babies' IL-6 values at birth. Conclusions: The patterns of CRP and IL-6 responses in the healthy neonate should be taken into account to optimize their use in the diagnosis of early-onset neonatal sepsis.