Pre-diabetes is increasingly common in the USA contributing to increased death independent of conversion to diabetes. Sub-types of pre-diabetes have been identified but little is known about the difference between them. Insulin action and secretion were assessed and compared in 3 sub-types of pre-diabetes using an intravenous glucose tolerance test (IVGTT). Subjects were classified as impaired fasting glucose (IFG, n=4) (fasting glucose 100-125 mg/dl, and 2h OGTT ≤140 mg/dl), impaired glucose tolerance (IGT, n=1) (fasting glucose ≤100 mg/dl, and 2h OGTT 140-200 mg/dl), or combined IFG/IGT (n=3) (fasting glucose 100-125 mg/dl, and 2h OGTT 140-200 mg/dl). Age (56 years), body mass index (BMI ˜30), and % fat (35.2%) were comparable between the groups. The first panel illustrates the insulin sensitivity index (ISI) IGT, IFG, IGT/IFG as determined by the IVGTT (20% dextrose bolus 0.3g/kg followed 20 min later by a bolus of regular insulin 0.03U/kg) and minimal model (MINMOD). Even with small numbers of subjects in this analysis, a trend toward higher insulin sensitivity in the IFG group is already being seen (IFG vs. IGT/IFG, p=0.17). The second panel depicts the acute insulin secretory response (AIR) adjusted for the amount of whole-body insulin action (the “disposition index” = AIR × ISI). Although not significantly different, a trend toward greater secretory response in the IFG vs. IGT/IFG group is noted. In summary, early trends imply greater insulin action and secretion in IFG vs. IFG/IGT. These findings challenge the prevailing paradigm, and highlight the importance of elaborating phenotypes of pre-diabetes.
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