Defining neonatal hypoglycaemia: a continuing debate.

Hypoglycaemia is one of the most frequent metabolic problems in neonatal medicine, and maintaining glucose homeostasis is one of the important physiological events during fetal-to-neonatal transition. Although frequently observed transient low blood glucose concentrations in the majority of healthy newborns are the reflections of normal metabolic adaptation processes during this transition, there has been a genuine concern that prolonged or recurrent low blood glucose levels may result in acute systemic effects and long-term neurological and developmental consequences. Hence, it is not surprising that neonatal hypoglycaemia remains one of the most important issues in our day-to-day practice and that we also become obsessed with the numbers and values that we believe are a 'cut-off' for its definition. The aim of this article is to critically appraise some of the available evidence either to support or refute the most widely accepted definition of 'neonatal hypoglycaemia' (blood glucose concentration: <2.6 mmol/l or 47 mg/dl), to highlight our knowledge gaps in defining neonatal hypoglycaemia, and to address the important concept of using an 'operational threshold', rather than focusing too much on a single blood glucose cut-off value, which is often applied to all newborn infants.