Shape of glucose, insulin, C-peptide curves during a 3-h oral glucose tolerance test: any relationship with the degree of glucose tolerance?
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, WHOSH(CP) (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. WHOSH(CP) (WHole-Ogtt-SHape-index) may be a powerful index of β-cell function much simpler than model-based indices.
Metabolic Unit, Institute of Biomedical Engineering, National Research Council, Padova, Italy. tura@isib.cnr.it
Andrea
A
Tura
Umberto
U
Morbiducci
Stefano
S
Sbrignadello
Yvonne
Y
Winhofer
Giovanni
G
Pacini
Alexandra
A
Kautzky-Willer
D000328:Adult; D001786:Blood Glucose / Q000378:metabolism*; D002096:C-Peptide / Q000097:blood*; D003924:Diabetes Mellitus, Type 2 / Q000097:blood / Q000503:physiopathology; D016640:Diabetes, Gestational / Q000097:blood / Q000503:physiopathology; D005260:Female; D018149:Glucose Intolerance / Q000097:blood / Q000503:physiopathology*; D005951:Glucose Tolerance Test / Q000145:classification; D006801:Humans; D007328:Insulin / Q000097:blood*; D050417:Insulin-Secreting Cells / Q000502:physiology; D011247:Pregnancy; D013997:Time Factors
D001786:Blood Glucose; D002096:C-Peptide; D007328:Insulin