Glycosylated hemoglobins and the oral glucose tolerance test in evaluation of glucose tolerance

: We performed OGTT and glycosylated hemoglobin (HbA1) determinations in 62 subjects. In those with IGT we noticed significantly increased average levels of HbA1 in comparison to normal or borderline ones, but 65.3% of the subjects with abnormal OGTT according to Fajans and Conn's criteria and 83.3% of those scored as borderline, had normal HbA1. This latter group showed a positive significant correlation with sum and peak of plasma glucose concentrations at 60 and 120 min during the test. Our opinion is that the mutual presence of abnormal OGTT and of increased HbA1 levels allows a reliable diagnosis of IGT, and the presence of normal HbA1 must induce us to suspect a false IGT diagnosis. 18 normal subjects showed, moreover, a remarkable HbA1 increase 30 days after the glucose load, with a return to basal levels after 40 days, while in 8 subjects with IGT, HbA1 remained constantly unmodified after 30 and 40 days. This is probably a consequence of a difference in daily glycemic profile between individuals with normal glucose tolerance and others with a reduced one.