Hypoglycemia and endogenous hyperinsulinism complicating diabetes mellitus. Application of the C-peptide assay to diagnosis and therapy.

Described here is a patient with insulin-requiring diabetes mellitus in whom spontaneous fasting hypoglycemia developed. Endogenous hyperinsulinism was considered after the systematic exclusion of other causes of hypoglycemia, and this possibility was confirmed by measurement of serum C-peptide reactivity (CPR), an indicator of beta cell secretory function. Subtotal pancreatectomy relieved the fasting hypoglycemia, and was associated with a marked decline in CPR levels. The pancreatic islets showed hyperplasia and the beta cells were degranulated.