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

Shape of glucose, insulin, C-peptide curves during a 3-h oral glucose tolerance test: any relationship with the degree of glucose tolerance? Am J Physiol Regul Integr Comp Physiol 300: R941-R948, 2011. First published January 11, 2011; doi:10.1152/ajpregu.00650.2010.--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 -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 -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-SHapeindex) may be a powerful index of -cell function much simpler than model-based indices. sha