Relationship Between β-Cell Function and Glycated Hemoglobin: Results from the Veterans Administration Genetic Epidemiology Study

• Published in: Diabetes care Vol. 34; no. 4; pp. 1006 - 1010
• Main Authors: Kanat, Mustafa, Winnier, Diedre, Norton, Luke, Arar, Nazik, Jenkinson, Chris, DeFronzo, Ralph A, Abdul-Ghani, Muhammad A
• Format: Journal Article
• Language: English
• Published: American Diabetes Association 01.04.2011
• Subjects: c-peptide; Dextrose; epidemiological studies; fasting; Genetic research; Glucose; glucose tolerance; Glucose tolerance tests; glycohemoglobin; Glycosylated hemoglobin; Insulin; Insulin resistance; insulin secretion; Mexican Americans; Original Research; Pancreatic beta cells; Veterans
• ISSN: 0149-5992; 1935-5548
• DOI: 10.2337/dc10-1352

OBJECTIVE: The study objective was to assess the relationship between β-cell function and HbA₁c. RESEARCH DESIGN AND METHODS: A total of 522 Mexican American subjects participated in this study. Each subject received a 75-g oral glucose tolerance test (OGTT) after a 10- to 12-h overnight fast. Insulin sensitivity was assessed with the Matsuda index. Insulin secretory rate was quantitated from deconvolution of the plasma C-peptide concentration. β-Cell function was assessed with the insulin secretion/insulin resistance (IS/IR) (disposition) index and was related to the level of HbA₁c. RESULTS: At HbA₁c levels <5.5%, both the Matsuda index of insulin sensitivity and IS/IR index were constant. However, as the HbA₁c increased >5.5%, there was a precipitous decrease in both the Matsuda index and the IS/IR index. Subjects with HbA₁c = 6.0-6.4% had a 44 and 74% decrease in the Matsuda index and the IS/IR index, respectively, compared with subjects with HbA₁c <5.5% (P < 0.01 for both indices). Subjects with normal glucose tolerance and HbA₁c <5.7% had β-cell function comparable to that of subjects with normal glucose tolerance with HbA₁c = 5.7-6.4%. However, subjects with impaired fasting glucose or impaired glucose tolerance had a marked decrease in β-cell function independent of their HbA₁c level. CONCLUSIONS: The results of the current study demonstrate that in Mexican Americans, as HbA₁c increases >6.0%, both insulin sensitivity and β-cell function decrease markedly. Performing an OGTT is pivotal for accurate identification of subjects with impaired β-cell function.