OBJECTIVE

To examine the levels of serum true insulin (TI) and proinsulin (PI) in individuals with different glucose tolerance and to assess its clinical significance.

METHODS

The levels of true insulin and proinsulin during oral glucose tolerance test (OGTT) were determined with specific BA-ELISA in 135 normal glucose tolerance (NGT) and 86 impaired glucose tolerance (IGT) subjects as well as 101 type II diabetes mellitus (DM) patients.

RESULTS

The fasting TI levels showed no significant difference (P > 0.05) among the groups of NGT, IGT and type II DM, but the immunoreactive insulin (IRI) concentration increased significantly in type II DM patients as compared with that in NGT (P < 0.01). Both of the fasting PI levels and the ratio of PI/(PI + TI) were significantly higher in type II DM patients as compared with those in NGT or IGT. The area under the curve of TI (AUC(TI)) was significantly higher (P < 0.05) in IGT than NGT and type II DM. Obese subjects had higher TI levels (P < 0.01) and lower insulin sensitivity (P < 0.05) than those in non-obese, while the ratio of PI/(PI + TI) and AUC(TI) was not significantly different statistically (P > 0.05) between the obese and non-obese subjects.

CONCLUSION

Type II DM patients present hyperproinsulinemia rather than hyperinsulinemia and have higher ratio of PI/(PI + TI) as compared with NGT and IGT subjects. Higher TI level and significant insulin resistance were observed in obese subjects, but there is no difference of the PI/(PI + TI) ratio. The fasting PI level and PI/(PI + TI) ratio tend to be the indexes of beta-cell dysfunction.