Plasma insulin concentration was measured during a standardized glucose infusion test (GIT) in 85 healthy subjects with a normal glucose tolerance and in 28 patients with manifest diabetes mellitus or decreased glucose tolerance. Each test was evaluated with the aid of an analogue computer model, and parameters characterizing different parts of the insulin curve during GIT were obtained. Large variations existed in all parameter values both in the normal and diabetic groups, and the overlapping between the two groups was considerable.
In 15 out of 85 healthy subjects the plasma insulin response during GIT was of the diabetic type as judged from the frequency distribution of the computer parameters (low values). The similarity was still more striking when the characteristics of the insulin curves in these 15 subjects were compared with those in patients with mild diabetes or with a decreased glucose tolerance only.
It is postulated that this type of low insulin response reflects a derangement of the release of insulin into the circulation, and that it marks an alteration which probably is a prerequisite for the development of diabetes mellitus. In this sense, these subjects may be considered to be potential diabetics.