Glucose Effectiveness from Short Insulin-Modified IVGTT and Its Application to the Study of Women with Previous Gestational Diabetes Mellitus

BACKGROUND: This study aimed to design a simple surrogate marker (i.e., predictor) of the minimal model glucose effectiveness (S(G)), namely calculated S(G) (CS(G)), from a short insulin-modified intravenous glucose tolerance test (IM-IVGTT), and then to apply it to study women with previous gestational diabetes mellitus (pGDM). METHODS: CS(G) was designed using the stepwise model selection approach on a population of subjects (n=181) ranging from normal tolerance to type 2 diabetes mellitus (T2DM). CS(G) was then tested on a population of women with pGDM (n=57). Each subject underwent a 3-hour IM-IVGTT; women with pGDM were observed early postpartum and after a follow-up period of up to 7 years and classified as progressors (PROG) or non-progressors (NONPROG) to T2DM. The minimal model analysis provided a reference S(G). RESULTS: CS(G) was described as CS(G)=1.06×10(−2)+5.71×10(−2)×K(G)/G(peak), K(G) being the mean slope (absolute value) of loge glucose in 10–25- and 25–50-minute intervals, and G(peak) being the maximum of the glucose curve. Good agreement between CS(G) and S(G) in the general population and in the pGDM group, both at baseline and follow-up (even in PROG and NONPROG subgroups), was shown by the Bland-Altman plots (<5% observations outside limits of agreement), and by the test for equivalence (equivalence margin not higher than one standard deviation). At baseline, the PROG subgroup showed significantly lower S(G) and CS(G) values compared to the NONPROG subgroup (P<0.03). CONCLUSION: CS(G) is a valid S(G) predictor. In the pGDM group, glucose effectiveness appeared to be impaired in women progressing to T2DM.