Role of beta-hydroxybutyrate measurement in the evaluation of plasma glucose concentrations in newborn infants.

Objective: The Glucose in Well Babies (GLOW) Study showed that there are two phases of low glucose concentrations in healthy newborn infants: an initial phase in which plasma concentrations of ketones are low; and a second phase in which low glucose concentrations are accompanied by elevated concentrations of ketones. The implications of these two phases for the brain differ depending on whether ketones are available as alternative substrate for brain metabolism. The purpose of this study was to estimate the duration of these two phases of neonatal low glucose concentrations in 66 healthy breastfed newborns from the GLOW Study during the first 5 days of life.

Methods: The sum of glucose and beta-hydroxybutyrate (BOHB) was used as a proxy for the total concentrations of insulin-dependent fuels for the brain; a threshold value below 4 mmol/L was taken to indicate the presence of relative hyperinsulinism and a BOHB concentration above 0.5 mmol/L to indicate ketonaemia.

Results: The first phase of low glucose concentrations lasted a median of 40 hours and in 15% of infants, this persisted beyond 60 hours. Fifty (76%) of the 66 infants subsequently had ketonaemia, which resolved at a median age of 76 hours (range 41->120 hours).

Conclusions: These data suggest that monitoring BOHB concentrations may be useful for interpreting glucose concentrations in newborns and screening for persistent hyperinsulinism.