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. 2012 Dec;35(12):2607-12.
doi: 10.2337/dc11-2504. Epub 2012 Aug 21.

Pathogenetic mechanisms and cardiovascular risk: differences between HbA(1c) and oral glucose tolerance test for the diagnosis of glucose tolerance

Cristina Bianchi  1 , Roberto Miccoli, Riccardo C Bonadonna, Francesco Giorgino, Simona Frontoni, Emanuela Faloia, Giulio Marchesini, Maria A Dolci, Franco Cavalot, Gisella M Cavallo, Frida Leonetti, Stefano Del Prato; GENFIEV Investigators
Collaborators, Affiliations

Pathogenetic mechanisms and cardiovascular risk: differences between HbA(1c) and oral glucose tolerance test for the diagnosis of glucose tolerance

Cristina Bianchi et al. Diabetes Care. 2012 Dec.

Abstract

Objective: To ascertain to which extent the use of HbA(1c) 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/m(2)) participated in this study. Parameters of β-cell function were derived from deconvolution of the plasma C-peptide concentration after a 75-g OGTT and insulin sensitivity assessed by homeostasis model 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 by OGTT and HbA(1c) were compared with 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 HbA(1c) 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 a worse 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: HbA(1c) 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.

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Figures

Figure 1
Figure 1
Insulin secretion by minimal model in NGT subjects by HbA1c and OGTT criteria (HbA1c−/OGTT−) compared with subjects meeting both criteria (HbA1c+/OGTT+) for prediabetes and individuals meeting only HbA1c (HbA1c+/OGTT−) or OGTT (HbA1c−/OGTT+) criteria. All measures are age-adjusted. A: Basal, prehepatic insulin secretion. B: β-Cell glucose sensitivity of derivative control (cognate of first-phase insulin secretion). C: Insulin secretion rate at 4.0, 5.5, 8.0, and 11.0 mmol/L glucose, by the stimulus-response curve, which defines glucose sensitivity of proportional control, cognate of second-phase insulin secretion. *P < 0.001 OGTT+/HbA1c+ vs. OGTT−/HbA1c−.
Figure 2
Figure 2
Association of HbA1c and OGTT categories with impaired insulin secretion (insulinogenic index <1st quartile of NGT subjects), IR (HOMA-IR >4th quartile of NGT subjects), and the metabolic syndrome. Odds ratio (OR) and 95% CI, adjusted for age, sex, and BMI.
See this image and copyright information in PMC

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