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

Authors: Pontiroli, A.1; Pizzocri, P.2; Caumo, A.3; Perseghin, G.4; Luzi, L.4

Source: Acta Diabetologica, Volume 41, Number 2, June 2004 , pp. 70-76(7)

Publisher: Springer

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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 ΔI/ΔG 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 ΔI/ΔG 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 ΔI/ΔG 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.

Keywords: Blood glucose; Diabetes; Euglycaemic clamp; Impaired glucose tolerance; Insulin release; Insulin sensitivity; Insulinogenic index; Oral glucose tolerance test

Document Type: Research Article

DOI: http://dx.doi.org/10.1007/s00592-004-0147-x

Affiliations: 1: Dipartimento di Medicina Interna, Ospedale San Paolo, Università di Milano, Via A. Di Rudini 8, I-20142, Milan, Italy, Email: antonio.pontiroli@unimi.it 2: Dipartimento di Medicina Interna, Ospedale San Paolo, Università di Milano, Via A. Di Rudini 8, I-20142, Milan, Italy, 3: Epidemiology and Statistical Service, Ospedale San Raffaele, Milan, Italy, 4: Divisione di Medicina, Ospedale San Raffaele, Milan, Italy,

Publication date: June 1, 2004

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