A1C Between 5.7 and 6.4% as a Marker for Identifying Pre-Diabetes, Insulin Sensitivity and Secretion, and Cardiovascular Risk Factors
The Insulin Resistance Atherosclerosis Study (IRAS)
- Carlos Lorenzo, MD1,
- Lynne E. Wagenknecht, DRPH2,
- Anthony J.G. Hanley, PHD3,
- Marian J. Rewers, MD4,
- Andrew J. Karter, PHD5 and
- Steven M. Haffner, MD6
- 1Department of Medicine, University of Texas Health Science Center, San Antonio, Texas;
- 2Division of Public Health Sciences, Wake Forest University School of Medicine, Winston-Salem, North Carolina;
- 3Nutritional Sciences and Medicine and Leadership, Sinai Centre for Diabetes, Mt. Sinai Hospital and the University of Toronto, Toronto, Ontario, Canada;
- 4Barbara Davis Center for Childhood Diabetes and Human Medical Genetics Program, University of Colorado Health Sciences Center, Aurora, Colorado;
- 5Division of Research, Kaiser Permanente, Northern California Region, Oakland, California;
- 6Department of Medicine, Baylor College of Medicine, Houston, Texas.
- Corresponding author: Carlos Lorenzo, lorenzo{at}uthscsa.edu.
Abstract
OBJECTIVE A1C is an optional method for diagnosing diabetes and also for detecting individuals at increased risk of the disease. However, how A1C compares with fasting (FPG) and 2-h plasma glucose for detecting at-risk individuals is not well known.
RESEARCH DESIGN AND METHODS A 2-h glucose tolerance test, frequently sampled intravenous glucose tolerance test, and A1C were obtained at the follow-up examination in 855 participants in the Insulin Resistance Atherosclerosis Study (IRAS). For this report, 385 individuals were at increased risk of diabetes as defined by A1C between 5.7 and 6.4%, impaired glucose tolerance (IGT), and/or impaired fasting glucose (IFG).
RESULTS IFG and IGT identified 69.1 and 59.5% of all individuals at increased risk of diabetes, respectively. A1C 5.7–6.4% detected 23.6% of all at-risk individuals, although more African Americans (31.4%) and Hispanics (35.2%) than non-Hispanic whites (9.9%). Relative to A1C, FPG was more strongly related to fasting insulin (r = 0.38 vs. 0.26; P < 0.01), acute insulin response (r = – 0.20 vs. – 0.09; P < 0.01), and waist circumference (r = 0.43 vs. 0.25; P < 0.001) by the Spearman correlation test. Similarly, 2-h plasma glucose was more strongly related to Si (r = – 0.40 vs. – 0.27; P < 0.01) and triglycerides (r = 0.30 vs. 0.08; P < 0.001).
CONCLUSIONS A1C 5.7–6.4% is less sensitive for detecting at-risk individuals than IFG and IGT, particularly among non-Hispanic whites. Single determinations of FPG and 2-h plasma glucose seem to be more precise correlates of insulin resistance and secretion than A1C and, in general, better for other metabolic disorders.
Footnotes
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- Received April 14, 2010.
- Accepted June 16, 2010.
- © 2010 by the American Diabetes Association.
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