The shape of the plasma glucose curve during an oral glucose tolerance test harbours information on whole body insulin sensitivity and β-cell function

Abstract

Background. Up to now, little attention has been devoted to the possible information related to the shape of the oral glucose tolerance test (OGTT) curve. Objective and hypotheses. We aimed to provide a classification and assessment of the prevalence of different shape types in postmenarcheal obese girls. It is hypothesized that the shape of the OGTT curve harbours valuable information on glucose metabolism. Methods. We investigated the shape of the OGTT curve in 72 postmenarcheal obese girls (agemean: 14.5 ± 1.4 years; BMI SDSmean: 2.8 ± 0.6). Plasma glucose and insulin concentrations were measured. OGTT-derived indices were calculated. Subjects were classified into three shapes of OGTT-curve: monophasic, biphasic or triphasic. Subjects with a shape index (G90’ – G120’) > 0 were defined as monophasic; a shape index (G90’ – G120’) < 0 as biphasic; or a shape index (G60’ – G90’) < 0 as triphasic. The presence of the metabolic syndrome was assessed according to the IDF criteria. Results. Most of the subjects showed a monophasic shape compared to bi- and triphasic shapes: 45.8, 37.5 and 16.6 %, respectively (χ² = 9.75; P = .008). The shape index was positively associated with BMI SDS (R² = 0.13 ; P = .002); gAUC (R² = 0.22; P = .000); HOMA-%B (R² = 0.05; P = .050) and the number of components of the metabolic syndrome. The shape index was inversely related to whole body insulin sensitivity index (R² = 0.06; P = .041). Conclusion. Subjects with a monophasic shape are at higher risk of having glucose abnormalities compared to subjects with a bi- or triphasic shape. A high shape index is indicative of increased pancreatic insulin secretion and low insulin sensitivity. Future and follow-up studies are needed to evaluate the usefulness of the shape of the OGTT curve to assess the risk for T2DM.