Objective: To determine the clinical significance of measuring serum true insulin (TI) in overweight and the non-obese with varying degrees of glucose tolerance, we estimated βeta cell (β- cell) function by calculating indices.
Methods: Serum true insulin, immunoreactive insulin (IRI), and glucose level in fasting and during an oral glucose tolerance test (OGTT) were measured in 32 individuals with normal glucose tolerance (NGT), 42 individuals with impaired glucose tolerance (IGT), 27 individuals with Type 1 diabetes mellitus (DM1), two-hour post-prandial glucose (2hPBG) ≤ 15 mmoL/L, 28 individuals with Type 2 diabetes mellitus (DM2), 2hPBG ≤ 20 mmoL/L, 29 individuals with Type 3 diabetes mellitus (DM3), 2hPBG ≤ 20 mmoL/L.
Results: The differences in βeta cell function among NGT, IGT, DM1, DM2, DM3 were apparent when, the ratio of the increasing serum insulin and plasma glucose levels after 60 minutes glucose loading (∆I60/∆G60) and the homeostasis model assessment-β-cell (HOMA-β) were calculated by TI and ∆I60/∆G60 which was calculated by IRI still decreased appropriately in NGT, IGT, DM1, DM2, DM3. However, the function of βeta cells was estimated in the overweight group higher than in the control group when evaluated by HOMA-β and modified beta cell function index (MβCI), but not by ∆I60/∆G60. We thought that ∆I60/∆G60 was a good choice when evaluating β-cell's secretory function, especially when TI could not be measured.
Conclusion: ∆I60/∆G60 was a widely used index which applied not only to diabetes but also to overweight.