Hemoglobin A1c and Mean Glucose in Patients With Type 1 Diabetes
Analysis of data from the Juvenile Diabetes Research Foundation continuous glucose monitoring randomized trial
- Darrell M. Wilson, MD1,
- Dongyuan Xing, MPH2,
- Roy W. Beck, MD, PHD2,
- Jennifer Block, RN, CDE1,
- Bruce Bode, MD3,
- Larry A. Fox, MD4,
- Irl Hirsch, MD5,
- Craig Kollman, PHD2,
- Lori Laffel, MD, MPH6,
- Katrina J. Ruedy, MSPH2,
- Michael Steffes, MD, PHD7,
- William V. Tamborlane, MD8 and
- Juvenile Diabetes Research Foundation Continuous Glucose Monitoring Study Group*
- 1Stanford University, Stanford, California
- 2Jaeb Center for Health Research, Tampa, Florida
- 3Atlanta Diabetes Associates, Atlanta, Georgia
- 4Nemours Children’s Clinic, Jacksonville, Florida
- 5University of Washington, Seattle, Washington
- 6Joslin Diabetes Center, Boston, Massachusetts
- 7University of Minnesota, Minneapolis, Minnesota
- 8Yale University, New Haven, Connecticut
- Corresponding author: Roy W. Beck, .
OBJECTIVE To determine the relationship between mean sensor glucose concentrations and hemoglobin A1c (HbA1c) values measured in the Diabetes Control and Complications Trial/Epidemiology of Diabetes Interventions and Complications laboratory at the University of Minnesota in a cohort of subjects with type 1 diabetes from the Juvenile Diabetes Research Foundation continuous glucose monitoring randomized trial.
RESEARCH DESIGN AND METHODS Near-continuous glucose sensor data (≥4 days/week) were collected for 3 months before a central laboratory–measured HbA1c was performed for 252 subjects ages 8–74 years, the majority of whom had stable HbA1c values (77% within ±0.4% of the patient mean).
RESULTS The slope (95% CI) for mean sensor glucose concentration (area under the curve) versus a centrally measured HbA1c was 24.4 mg/dL (22.0–26.7) for each 1% change in HbA1c, with an intercept of −16.2 mg/dL (−32.9 to 0.6). Although the slope did not vary with age or sex, there was substantial individual variability, with mean sensor glucose concentrations ranging from 128 to 187 mg/dL for an HbA1c of 6.9–7.1%. The root mean square of the errors between the actual mean sensor glucose concentration versus the value calculated using the regression equation was 14.3 mg/dL, whereas the median absolute difference was 10.1 mg/dL.
CONCLUSIONS There is substantial individual variability between the measured versus calculated mean glucose concentrations. Consequently, estimated average glucose concentrations calculated from measured HbA1c values should be used with caution.
- Received June 3, 2010.
- Accepted December 17, 2010.
- © 2011 by the American Diabetes Association.
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