As a follow on to the previous post, also to highlight a thoughtful review article, we could ask whether blood sugar can be too low to be good for you (I think there is not much doubt about that) how to define hypoglycemia (probably varies according to the context) how to diagnose it (may take more than a blood sugar, and certainly not a bedside strip test) and whether it helps to treat it (only if you get the diagnosis right, can probably cause harm when you treat a normal baby).
The review in question (Hawdon JM: Definition of neonatal hypoglycaemia: Time for a rethink? Archives of disease in childhood Fetal and neonatal edition 2013.) points out that when metabolic adaptation is intact babies can mobilize and use other sources of energy, and probably don’t need intervention at all, even if the blood sugar is as low as 1 mmol/L. She also notes that babies with hyperinsulinism have these adaptations completely suppressed.
So here is the problem, how to identify those babies that have intact adaptation mechanisms, and those that don’t. Because a proportion of babies with normal or low birth weight will have hyperinsulinism, not just the obvious infant of a diabetic mother. I am not sure that deciding if the infant is symptomatic is very good at differentiating either, the symptoms often listed are so non-specific that almost any baby could be symptomatic. Perhaps what we really need is a quick simple reliable point-of-care test of blood sugar which is combined with indicators of adequate metabolic response, or insulin levels. Many babies are currently getting screened and treated, only a proportion of which are probably benefiting. I think that is probably the best we can do for the moment, but we need to pursue this further for the future.