Insulin, C-peptide and proinsulin for the biochemical diagnosis of hypoglycaemia related to endogenous hyperinsulinism

Abstract

Proinsulin levels above 5 pmol/l with blood glucose levels below 2.5 mmol/l during a 72 h fast test represent the best criterion for the diagnosis of endogenous hyperinsulinism, reaching 100% diagnostic specificity and sensitivity. Concomitant C-peptide levels above 0.2 nmol/l also make the diagnosis of all our insulinoma patients, not the diagnosis of nesidioblastosis, while insulin levels have much less diagnostic accuracy. Whether proinsulin levels above 22 pmol/l could also make the diagnosis of endogenous hyperinsulinism in part of the patients at the time of fasting blood glucose levels between 2.5 and 3.3 mmol/l or after an overnight fast in non-obese subjects needs further study.