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

  1. Juvenile Diabetes Research Foundation Continuous Glucose Monitoring Study Group*
  1. 1Stanford University, Stanford, California
  2. 2Jaeb Center for Health Research, Tampa, Florida
  3. 3Atlanta Diabetes Associates, Atlanta, Georgia
  4. 4Nemours Children’s Clinic, Jacksonville, Florida
  5. 5University of Washington, Seattle, Washington
  6. 6Joslin Diabetes Center, Boston, Massachusetts
  7. 7University of Minnesota, Minneapolis, Minnesota
  8. 8Yale University, New Haven, Connecticut
  1. Corresponding author: Roy W. Beck, jdrfapp{at}


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.

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  1. Diabetes Care
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