Insulin Patterns in Equivocal Glucose Tolerance Tests (Chemical Diabetes)

Hyperinsulinemic patterns are a well recognized feature of equivocal glucose tolerances of the chemical diabetes type, i.e. those that are neither definitely nondiabetic nor clearly diabetic. A more complete characterization of such insulin responses is obtained when the data are expressed in terms of increments in insulin from the zero time point. Thus, two patterns of insulin increments after oral glucose become evident when the equivocal zone of glucose tolerance is divided into lower and upper segments. Tests in the lower segment show normal increments at the halfhour point of the test; at one hour these tests show excessive increments which persist throughout the five hours of observation. On the other hand, tests in the upper zone show delays in the serum insulin rise at the half-hour point, followed by normal increments at one hour and excessive increments thereafter. The pattern is the same whether or not obesity is present. It is suggested that tests in the equivocal zone of Glucose Tolerance Sum values be taken to be indicative of chemical diabetes. Tests with the Sum in the lower half of the equivocal zone could then represent chemical diabetes with mild intolerance stemming from insulin ineffectiveness, since insulin increments in this group are at or above the mean values recorded in nondiabetic controls. On the other hand, chemical diabetes with moderate glucose intolerance and Glucose Tolerance Sums in the upper half of the equivocal zone would be understood to result from a combination of an initial delay in the serum insulin rise followed by normal and then excessive increments in serum insulin with the latter two indicative of insulin ineffectiveness. However, insulin ineffectiveness may also be present at the time of the insulin delay. High glucose:insulin ratios in tests indicative of chemical diabetes are almost always attributable to higher glucose increments with insulin increments normal or excessive compared to normal glucose tolerances. Deficient insulin increments contribute to the high ratios only at the half-hour point in tests with Glucose Tolerance Sums in the upper zone of equivocal glucose tolerances.