L'utilità dell'oral glucose tolerance test nella diagnosi di diabete mellito

Diagnostic criteria for diabetes mellitus from fasting glycemia introduced on 1997 by the American Diabetes Association (ADA) modified the prevalence of diabetes, as well as that of prediabetes which were previously based on the oral glucose tolerance test (OGTT). In the following years a lot of trials agreed in demonstrating that the only baseline blood glucose would result in underestimation of diabetes, even in a relevant manner. At the same time the two classes defined as "impaired fasting glucose" (IFG) by means of fasting glycemia and as "impaired glucose tolerance" (IGT) by OGTT proved to not overlap. IGT was more sensitive in predicting the appearance of diabetes, the overall mortality from any cause and that due to cardiovascular disease. All the above mentioned evidences led the ADA to modify on 2003 the previously suggested diagnostic criteria. The cut-off value of baseline glycemia was lowered from 110 to 100 mg/dl and the values under 100 mg/dl are to be considered as normal. However this caused the inclusion in prediabetes millions of subjects who were considered healthy by the previous classification. An open problem is the underestimation of the prevalence of diabetes, as after 1997 ADA did not modify the baseline glycemic cut-off level. Up to now the OGTT maintains its usefulness in the diagnosis of diabetes mellitus, as a higher diagnostic sensitivity when compared to fasting glycemia has been clearly demonstrated.