Objective:To study the changes of true insulin(TI) and immunoreactive insulin (IRI) in subjects with NGT, IGT and DM, to study the difference between true insulin and immunoreactive insulin in evaluating βcell function and insulin sensitivity. Methods:The levels of serum IRI and TI were determined in 54 cases with type Ⅱ diabetes mellitus(Group DM) ,43 cases with impaired glucose tolerance (Group IGT) and 75 cases with normal glucose tolerance (Group NGT). Then every group was subdivided into obese and non - obese subgroups according to body mass index. IRI was determined by RIA. TI was determined by ELISA using monoclonal antibody with no significant cross- reaction between insulin and proinsulin. The insulin resistance index (Homa- IR), pancreatic β- cell function index (Homa- B) and insulin release index (the ratio of the increment of insulin to that of plasma glucose 30 min after a glucose load,△ I30/△G30) were analyzed preliminarily. Results: The ratio of TI/IRI in non - obese subgroup with DM was lower than those in non obese subgroups with NGT and IGT (P＜0.01). The ratios of TI/Ipd in obese subgroups with IGT and DM were lower than those in obese subgroup with NGT(P＜0.05). The pancreatic β-cell function indexes (Homa-BIRI) of IRI in non- obese subgroups with IGT and DM were lower than that in non- obese subgroup with NGT(P＜0.05). The pancreatic β - cell function index (Homa- BTI) of TI in non- obese subgroup with IGT was lower than that in non obese subgroups with NGT ( P ＜ 0.05 ). The HomaBTI in non - obese subgroup with DM was lower than that in non - obese subgroups with NGT and IGT(P ＜0.01).The Homa - BIRI in obese subgroups of NGT, IGT and DM had no significant difference. Homa - BTI in obese subgroups with IGT and DM was lower than that in obese subgroup with NGT(P＜0.01). Conclusion:The ratio of TI/IRI was a good marker in evaluating β- cell function. Pancreatic β- cell function index (Homa- BTI) of TI was better than that of IRI.
