title: Evaluation of insulin release and insulin sensitivity through oral glucose tolerance test: differences between NGT, IFG, IGT, and type 2 diabetes mellitus. A cross-sectional and follow-up study.
abstract: We evaluated both insulin release (IR) and insulin sensitivity (IS) through a single oral glucose tolerance test (OGTT) (blood samples at 0, 60, 120 min, as routinely performed in Europe) in subjects with normal and abnormal glucose tolerance. The value 1/HOMA was used as an index of IS and deltaI/deltaG at 60 min was used as an index of IR. In preliminary experiments, 1/HOMA correlated with glucose infusion rate (GIR) at euglycaemic insulin clamp (r=0.495) and with insulin sensitivity index (ISI) at LDIGIT (r=0.714). At OGTT with blood samples at 0, 30, 60 and 120 min, insulin levels at 30 min correlated with insulin levels at 60 min (I30 vs. I60, r=0.584) and deltaI/deltaG at 30 and at 60 min correlated (r=0.365). Values of 1/HOMA from 345 subjects with normal glucose tolerance (NGT), 32 with impaired fasting glucose (IFG), 186 with impaired glucose tolerance (IGT) and 72 with type 2 diabetic mellitus were divided into quartiles. For each quartile, mean (+/- SE) and 95% confidence intervals (CI) of deltaI/deltaG at 60 min were calculated, and subjects were represented by plotting IS vs. IR. Plots of NGT, IGT, and type-2 diabetes mellitus described different curves. Values of subjects with IFG, IGT and type 2 diabetes mellitus fell outside the 95% CI of NGT subjects in all quartiles of IS. To validate this finding, 113 morbidly obese subjects (basal OGTT: 55 NGT, 40 IGT, 18 T2DM) who underwent a major reduction of body weight through bariatric surgery received a second OGTT one year after surgery. Glucose tolerance improved in 40 patients, deteriorated in 8, did not change in 65; the new plots were concordant with the new class of glucose tolerance. OGTT can be used to evaluate both IR and IS in subjects with NGT, IFG, IGT, and type 2 diabetes mellitus in population studies and in follow-up studies. IFG, IGT and type 2 diabetes mellitus are characterized by reduced IR compared to IS.
authors.affiliation: Dipartimento di Medicina Interna, Ospedale San Paolo, Università di Milano, Via A. Di Rudini 8, I-20142, Milan, Italy. antonio.pontiroli@unimi.it
authors.forename: A E
authors.initials: AE
authors.lastname: Pontiroli
authors.forename: P
authors.initials: P
authors.lastname: Pizzocri
authors.forename: A
authors.initials: A
authors.lastname: Caumo
authors.forename: G
authors.initials: G
authors.lastname: Perseghin
authors.forename: L
authors.initials: L
authors.lastname: Luzi
mesh_terms: D000328:Adult; D001786:Blood Glucose / Q000032:analysis / Q000378:metabolism*; D015992:Body Mass Index; D003430:Cross-Sectional Studies; D003924:Diabetes Mellitus, Type 2 / Q000097:blood* / Q000503:physiopathology; D005215:Fasting; D005500:Follow-Up Studies; D005951:Glucose Tolerance Test / Q000379:methods*; D006801:Humans; D007328:Insulin / Q000097:blood / Q000378:metabolism*; D000078790:Insulin Secretion; D008954:Models, Biological; D012044:Regression Analysis
chemical_list: D001786:Blood Glucose; D007328:Insulin