Pathogenetic mechanisms and cardiovascular risk: Differences between HbA1c and oral glucose tolerance test for the diagnosis of glucose tolerance

OBJECTIVE To ascertain to which extent the use of HbA1c and oral glucose tolerance test (OGTT) for diagnosis of glucose tolerance could identify individuals with different pathogenetic mechanisms and cardiovascular risk profile. RESEARCH DESIGN AND METHODS A total of 844 subjects (44%men; age 49.5 +- 11 years; BMI 29 +- 5 kg/m2) participated in this study. Parameters of b-cell functionwere derived from deconvolution of the plasma C-peptide concentration after a 75-g OGTT and insulin sensitivity assessed by homeostasismodel assessment of insulin resistance (IR). Cardiovascular risk profile was based on determination of plasma lipids and measurements of body weight, waist circumference, and blood pressure. Glucose regulation categories byOGTT and HbA1c were comparedwith respect to insulin action, insulin secretion, and cardiovascular risk profile. RESULTS OGTT results showed 42% of the subjects had prediabetes and 15% had type 2 diabetes mellitus (T2DM), whereas the corresponding figures based on HbA1c were 38 and 11%, with a respective concordance rate of 54 and 44%. Subjects meeting both diagnostic criteria for prediabetes presented greater IR and impairment of insulin secretion and had aworse cardiovascular risk profile than those with normal glucose tolerance at both diagnostic methods. In a logistic regression analyses adjusted for age, sex, and BMI, prediabetic subjects, and even more T2DM subjects by OGTT, had greater chance to have IR and impaired insulin secretion. CONCLUSIONS HbA1c identifies a smaller proportion of prediabetic individuals and even a smaller proportion of T2DM individuals than OGTT, with no difference in IR, insulin secretion, and cardiovascular risk profile. Subjects fulfilling both diagnostic methods for prediabetes or T2DM are characterized by a worse metabolic profile.