Plasma proinsulin and C-peptide concentrations in children with hyperinsulinaemic hypoglycaemia.

Plasma concentrations of proinsulin and C-peptide were measured in five children presenting with severe hypoglycaemia associated with elevated plasma levels of immunoreactive insulin (IRI) in order to determine whether the profile of circulating B-cell products related to the underlying pathophysiology of the pancreas. Results were compared with data from 13 normal infants. Four children, three neonates and a nine year old girl, were subjected to partial or total pancreatectomy. The neonates had nesidioblastosis, nesidioblastosis with a microadenoma, and a functional abnormality without histological derangement respectively; the older child had a localised adenoma. The remaining child, a neonate, had transient hypoglycaemia and elevated IRI levels associated with hyperlactataemia and hyperalaninaemia. All the children had markedly elevated plasma proinsulin concentrations; the highest levels were seen in the child with an isolated adenoma and in the neonate with nesidioblastosis and a microadenoma. Both of these children also had substantially elevated plasma C-peptide concentrations. The remaining three neonates had plasma C-peptide levels, which although in the normal range for normoglycaemia were inappropriately elevated during hypoglycaemia. It is concluded that elevated proinsulin and C-peptide concentrations are seen in children with hypoglycaemia associated with increased plasma IRI levels and that the profile of the concentrations does not provide a reliable marker for the nature of the underlying pancreatic abnormality.