Insulin secretion in the diagnosis of adult-onset diabetes mellitus.

The natural history of patients with glucose intolerance was observed in 334 patients during a period of 18 years. Glucose tolerance testing (100 g orally) was characterized by measurement of induced insulin secretion. Diabetic complications of retinopathy, sensory neuropathy, and renal disease developed only in the group of patients in whom the induced serum insulin peak fell below 60 mu U/ml. Preservation of an insulin secretory reserve that permitted serum insulin peaks of 60 muU/ml or greater was not associated with development of these complications or symptoms of insulin deficiency despite the presence of an equal degree of fasting hyperglycemia and glucose intolerance. A critical amount of insulin secretory reserve distinguishes between two qualitatively distinct clinical syndromes: true diabetes mellitus (the development of signs and symptoms of insulin deficiency) and the syndrome of pure resistance to insulin (signs and symptoms of hyperglycemia in the setting of adequate or excessive insulin secretion, frequently with obesity, but without diabetic complication).