Insulin and Glucose Responses to Identical Oral Glucose Tolerance Tests Performed Forty-eight Hours Apart

We compared the plasma glucose and insulin responses to two identical oral glucose tolerance tests performed forty-eight hours apart in thirty-one adult patients. The mean results of the two tests were essentially identical, indicating that no consistent difference in glucose or insulin response occurs upon repetitive oral glucose tolerance testing. When the variability of the glucose response curves were analyzed by comparing repeat values to each other, it was found that nine of thirty-one fasting values deviated by more than 10 per cent, but no fasting values deviated by more than 30 per cent. The one hour value was more variable: Twenty-two of thirty-one observations deviated by more than 10 per cent and six of thirty-one deviated by more than 30 per cent. The variability of the insulin response was greater. For example, fourteen of thirtyone fasting values deviated by more than 10 per cent, and three of thirty-one deviated by more than 30 per cent, while twenty-six of thirty-one one hour values deviated by more than 10 per cent and twenty-one of thirty-one deviated by more than 30 per cent. Furthermore, the ratio of the insulin response to the glucose response (I/G ratio) was as variable as was the insulin response alone. The extreme variability of the insulin response to identical glucose loads, coupled with similar variability of the I/G ratio, suggests that factors other than glucose concentration play a role in regulating insulin response.