It has been known for some time that some SGA babies with hypoglycemia are hyperinsulinemic. As many as 20% of some small series have shown this phenomenon, they can be suspected because of the high glucose requirements, and confirmed, I thought, but measuring insulin concentrations during a hypoglycemia. I now find out that sometimes babies who have hyperinsulinemic hypoglycemia aren’t all hyperinsulinemic when they are hypoglycemic. (try saying that quickly after a glass of wine).
I have seen this in practice, a baby who needs a lot of sugar, is probably hyperinsulinemic but has low or undetectable insulin when hypoglycemic, I didn’t know previously how to interpret it, but it seems that it is not uncommon. I guess the insulin level is too high when the sugar is normal, but when they get hypoglycemic they are able to suppress insulin production to below the sensitivity of the lab tests.
In these circumstances other indications of hyperinsulinism, such as very low free fatty acids, low beta-hydroxybutyrate, or an exaggerated glucose response to glucagon can confirm the diagnosis. (Hoe FM, Thornton PS, Wanner LA, Steinkrauss L, Simmons RA, Stanley CA: Clinical features and insulin regulation in infants with a syndrome of prolonged neonatal hyperinsulinism. The Journal of pediatrics 2006, 148(2):207-212.)
This new publication (Arya VB, Flanagan SE, Kumaran A, Shield JP, Ellard S, Hussain K, Kapoor RR: Clinical and molecular characterisation of hyperinsulinaemic hypoglycaemia in infants born small-for-gestational age. Archives of Disease in Childhood – Fetal and Neonatal Edition 2013.) examined whether there were abnormalities in the genes regulating insulin secretion, genes that may be abnormal in the permanent types of hyperinsulinemic hypoglycemia. There weren’t.
In these SGA babies with the condition it is transient, although it may last some months, and the new publication lets you know that a) these babies respond well to diazoxide, and b) when you can get the diazoxide dose below 5 mg/kg/day you can safely stop it.
So we need to measure these other indicators of hyperinsulinism if a hypoglycemic baby who needs a high glucose infusion rate needs further diagnostic testing.