Shape of glucose, insulin, C-peptide curves during a 3-h oral glucose tolerance test: any relationship with the degree of glucose tolerance?

Abstract

We aimed to analyze the shape of the glucose, insulin, and C-peptide curves during a 3-h oral glucose tolerance test (OGTT). Another aim was defining an index of shape taking into account the whole OGTT pattern. Five-hundred ninety-two OGTT curves were analyzed, mainly from women with former gestational diabetes, with glycemic concentrations characterized by normal glucose tolerance ( n = 411), impaired glucose metabolism ( n = 134), and Type 2 diabetes ( n = 47). Glucose curves were classified according to their shape (monophasic, biphasic, triphasic, and 4/5-phases), and the metabolic condition of the subjects, divided according to the glucose shape stratification, was analyzed. Indices of shape based on the discrete second-order derivative of the curve patterns were also defined. We found that the majority of the glucose curves were monophasic ( n = 262). Complex shapes were less frequent but not rare ( n = 37 for the 4/5-phases shape, i.e., three peaks). There was a tendency toward the amelioration of the metabolic condition for increasing complexity of the shape, as indicated by lower glucose concentrations, improved insulin sensitivity and β-cell function. The shape index computed on C-peptide, WHOSHCP (WHole-Ogtt-SHape-index–C-peptide), showed a progressive increase [monophasic: 0.93 ± 0.04 (dimensionless); 4/5-phases: 1.35 ± 0.14], and it showed properties typical of β-cell function indices. We also found that the type of glucose shape is often associated to similar insulin and C-peptide shape. In conclusion, OGTT curves can be characterized by high variability, and complex OGTT shape is associated with better glucose tolerance. WHOSHCP (WHole-Ogtt-SHape-index) may be a powerful index of β-cell function much simpler than model-based indices.

The Shape of the Glucose Response Curve During an Oral Glucose Tolerance Test Heralds Biomarkers of Type 2 Diabetes Risk in Obese Youth

“…Studies in adults established the concept of the OGTT-glucose response curve (i.e., monophasic vs. biphasic) and subsequently supported that the shape of the monophasic response represents an increased risk for type 2 diabetes through cross-sectional studies (4,29–31). The findings from these cross-sectional studies were further confirmed longitudinally, showing that over a 7- to 8-year follow-up period the conversion rate to type 2 diabetes in prediabetic adults with a monophasic glucose response was nearly double those with a biphasic glucose response (5).…”

“…Previous studies reported that the shape of the monophasic response is the dominant phenotype, with prevalence ranging (after excluding the unclassified group) from 57% to 84% in adults (4,5,29–31) and from 35% to 69% in youth (14–16). Based on our present study and other pediatric studies (15) showing, in general, higher biphasic response curve rates than those in adults, together with publications concerning adults, that a biphasic response is associated with younger age compared with the monophasic response (4), it could be postulated that the aging process may have a negative impact on the glucose response curve.…”

Estimating the risk after gestational diabetes mellitus: can we improve the information from the postpartum OGTT?

“…This is in accordance with previous studies that have proved that all of the samples of the OGTT, and not only the fasting and 2-h values, may yield relevant clinical information. Specifically, it was proved that the shape of the OGTT curves (glucose, but also insulin and C-peptide) is related to the subject's metabolic condition (34). In particular the variability of the OGTT curves is related to the degree of glucose tolerance.…”

Inside out the Ragbag of Glucose Intolerance in Obese Adolescents

“…Similar parameters were computed by using C-peptide instead of insulin. Furthermore, we calculated the C-peptide-based shape index, which has been found to be another parameter of β-cell function [25]. …”