Insulin resistance and beta-cell dysfunction in people with prediabetes according to criteria based on glycemia and glycosylated hemoglobin.

Impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) are well-known conditions of risk for diabetes. Recently, 1h-hyperglycemia (1h-HG), i.e., glycemia > 8.6 mmol/L, has been suggested as further condition of diabetes risk. Moreover, in 2010 the American Diabetes Association included the measurement of glycosylated hemoglobin (HbA1c) among the criteria of diabetes risk (5.7-6.4%). Aim of this study was investigating all these different conditions of diabetes risk, with specific focus on possible insulin sensitivity and beta-cell function changes, when 1h-HG, and further HbA1c-prediabetes, are added to the already deeply studied condition of IFG/IGT. In this study, we retrospectively analysed 744 participants that underwent 2h-OGTT and HbA1c measurement. Participants were stratified into groups: (i) normal glucose tolerance, NGT (n=178); (ii) IFG and/or IGT (n=88); (iii) IFG/IGT plus 1h-HG (n=342); (iv) IFG/IGT plus 1h-HG plus HbA1c-prediabetes (n=136). We calculated several indices of insulin sensitivity and beta-cell function, as well as an index considering both aspects (disposition index). We found that progressing from group (i) to group (iv) both insulin sensitivity and beta-cell function tended to further deteriorate; the parameter providing more evidence was the disposition index (p<0.008 in any group comparison). In conclusion, for appropriate assessment of the level of diabetes risk (especially in people already known to be at high risk), it may be convenient to measure all the indicated parameters, that is, glycemia at fasting, at one hour and two hours during OGTT, and glycosylated hemoglobin.