The diagnosis of insulinomas and other causes of fasting hypoglycemia.

The decrease in insulin secretion in normal subjects in response to hypoglycemia provides a basis for suppression tests for diagnosing insulinomas. The majority of patients with insulinomas have hypoglycemia after an overnight fast, and inordinatley raised plasma insulin levels are diagnostic. A prolonged fast is a means of enhancing hypoglycemia. Fish insulin can be used to induce hypoglycemia over a short period, and provides a simple, dynamic suppression test which appears to give good diagnostic discrimination. A normal endogenous insulin response to fish-insulin-induced hypoglycemia, together with clinical assessment and a few simple investigations, virtually excludes the diseases which cause fasting hypoglycemia in adults.