Use of an automatic blood glucose measurement system for the assessment of insulin resistance during the oral glucose tolerance test

An automatic glycemic control system (Beta-like, Esaote) was used to calculate the insulin area (IA) required to keep glycemia within the normal range during OGTT (using NDDG criteria). IA was calculated by adding total endogenous insulin to insulin infused by the Betalike system (Actrapid HM, Novo). During the test, glycemia was obliged to follow a mean normal curve using an insulin infusion according to a special algorithm which automatically adapted to individual parameter variations during the different stages of OGTT. Fourteen blood samples were collected to assay metabolites (glucose, NEFA, lactate and alanine) and hormones (insulin, C peptide, glucagon). Data on insulinemia and glycemia were used to calculate the respective areas under the total and incremental curve (IA expressed in UL-1 min-1 and GA expressed in mM.L-1.min-1); an insulin resistance index was then calculated (total and incremental) using the following formula: IA/(normal GA/patient GA). This test allows us: a) to evaluate the insulin secretory response to a standard glycemic stimulus represented by a glycemic curve within the normal range; b) to calculate the quantity of insulin necessary to maintain the glycemic curve within the normal range; c) to evaluate the body's total insulin resistance according to an index calculated on the basis of the insulin area required; d) to compare the calculated insulin resistance index with NEFA and glucagon data obtained during the test; e) to identify the exact evolution of these events over time during OGTT.