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The shape of the glucose curve and time to glucose peak during an oral glucose tolerance test as indicators of beta cell function in obese adolescents

Introduction: Morphological characteristics of the glucose concentration curve during an oral glucose tolerance test (OGTT) may reflect differences in insulin secretion and sensitivity. Whether the shape of the glucose curve and time to peak glucose concentration can be used as indicators of beta cell function and markers of type 2 diabetes risk in obese adolecents is still uncertain. Aims/hypothesis: The purpose of this cross-sectional study was to assess whether the shape of the glucose response curve (monophasic vs biphasic) and timing of the post challenge peak blood glucose (30 vs ≥60 min) during OGTT can be indicators of beta cell function in obese adolescents with normal glucose tolerance (NGT). We hypothesised that monophasic glucose curve and delayed timing of peak glucose (≥60 min) are independently associated with impaired beta cell function estimated through oral disposition index (oDI). Research design and methods: A total of 159 obese adolescents who completed a 2-h OGTT and were classified as NGT, were further categorised by the glucose curve shape as either a monophasic or a biphasic group, or by the time to maximal glucose concentration as either a group with early (30 minutes) or late glucose peak (≥60 minutes). Groups were compared with respect to insulin sensitivity (whole body insulin sensitivity index, WBISI), early-phase insulin secretion (insulinogenic index, IGI) and beta cell function (oral disposition index, oDI). Results: 84 (52.8%) adolescents had a monophasic and 75 (47.2%) a biphasic curve shape. Participants with monophasic curve had lower IGI (p=0.001) and poorer beta cell function relative to insulin sensitivity as reflected by lower oDI (p<0.001) compared with the biphasic curve group. No differences were found in the degree of obesity (BMI z-score) between groups, but participants in the biphasic group were younger (p=0.001), with higher proportion of prepubertal and early pubertal subjects and male predominance. With respect to glucose peak, 92 (57.9%) participants had an early and 67 (42.1%) a late peak. The latter group had lower IGI (p=0.038) and lower oDI (<0.001). There were no significant differences between early and late glucose peak groups in the degree of obesity, puberty stage and gender, but subjects with late glucose peak were older (p=0.03). Conclusion: Among obese adolescents with NGT, those with monophasic curve shape as well as those with glucose peak ≥60 minutes during an OGTT, are at increased risk of beta cell dysphunction.

oral glucose tolerance test ; glucose curve shape ; time to glucose peak ; obese adolescents

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