Blood levels of true insulin and immunoreactive insulin in evaluating beta-cell function with arginine stimulation test

Abstract

To investigate the difference between serum true insulin (TI) and immunoreactive insulin (IRI) in evaluating islet beta-cell function and insulin resistance. The arginine stimulation test was performed in 141 individuals, including 35 with normal glucose tolerance (NGT) and 106 with type 2 diabetes (T2DM). Plasma glucose (PG), TI, IRI and proinsulin (PI) levels were measured; the incremental value of TI/PG, (TI+PI)/PG and IRI/PG (delta TI/PG, delta(TI+PI)/PG and deltaIRI/PG) and the area under curve of TI/PG, (TI+PI)/PG and IRI/PG (AUC [TI/PG], AUC[(TI+PI)/PG] and AUC [IRI/PG]) after arginine stimulation were calculated to evaluate beta-cell function. There were positive correlations of delta TI/PG with delta (TI+PI)/PG and delta IRI/PG in both NGT and T2DM patients (r=0.68 - 0.99, P<0.01). The similar correlations of AUC [TI/PG] with AUC [(TI+PI)/PG] and AUC [IRI/PG] were also shown (r=0.62 - 0.99, P<0.01). delta TI/PG was correlated with AUC [TI/PG] in two groups (NGT r=0.96, T2DM r=0.82, P<0.01). HOMA-IRTI, HOMA-IR(TI+PI) and HOMA-IRIRI in T2DM were higher than those in NGT (P<0.01). After arginine stimulation T2DM subjects mainly presented insulin resistance and decreased insulin secretion. The determination of TI may be more accurate than IRI in evaluating beta-cell function and insulin resistance.