Control of basal insulin secretion, with special reference to the diagnosis of insulinomas.

Estimation of plasma glucose and immunoreactive insulin concentrations in normal subjects after an overnight fast showed that subjects with high basal plasma glucose levels tended to have high plasma insulin concentrations. A similar correlation between glucose and insulin levels was seen in patients with obesity and various endocrine disorders. The suppression of plasma insulin levels associated with hypoglycaemia was used to derive an "amended insulin-glucose ratio," which appeared to be a good discriminant for the diagnosis of insulinomas. In normal subjects the ratio was less than 30 muU insulin/mg glucose, in obese subjects less than 50 muU/mg, and most of the patients with insulinomas had values over 200 muU/mg.