Long-term repeatability of measures of early insulin secretion derived from an intravenous glucose tolerance test and conversion from impaired glucose tolerance to diabetes.

Aim: We assessed the long-term repeatability of the acute insulin response (AIR) and sensitivity index (S(I)) derived from the frequently sampled intravenous glucose tolerance test (FSIGT).

Methods: An FSIGT was performed in 20 women who participated in a 6.5-month rye- and wheat-bread intervention trial, 70 men and women with impaired fasting glycaemia (IFG) or impaired glucose tolerance (IGT) who participated in the Genobin study, and 81 men and women with IGT who participated in the Finnish Diabetes Prevention Study (DPS).

Results: The correlation of AIR and S(I) at base-line with respective values after the 6.5-8.5-month trials was 0.86-0.88 and 0.71-0.84, and before and after 4 years in the DPS substudy, 0.86 and 0.53. In multivariate analyses, AIR (relative risk for a 1-SD change, 0.67; 95% confidence intervals 0.46-0.97) predicted the conversion from IGT to diabetes in the DPS substudy.

Conclusion: AIR is highly repeatable even after 4 years of follow-up. The long-term repeatability of S(I) is moderate. Our findings emphasize the importance of impaired early insulin secretion in the transition from IGT to diabetes, and the high degree of tracking of measures of early insulin secretion derived from the FSIGT.