The incidence of impaired carbohydrate tolerance is greater with increasing age, in pregnancy, obesity, acromegaly, thyrotoxicosis, uremia, myocardial infarction, and hepatic disease. The differential diagnosis of diabetes mellitus presents special problems in the presence of these disorders.
The determination of plasma insulin or serum insulin-like activity (ILA) in the fasting state or during a glucose tolerance test has been done in patients with the above conditions and has shed some new light on the mechanisms of the associated abnormalities noted in glucose tolerance. Plasma insulin may be determined by a radio-immunological method (which gives the lowest, but most specific estimate) or by a method which measures total serum ILA in the rat diaphragm or fat pad. In general, the rise of blood insulin during the oral glucose tolerance test (OGTT) is greater but the peak value is later than that seen during an intravenous glucose tolerance test.
On average, in