Hemoglobin A1c and the Estimated Average Glucose

Limitations

July 2009

There are some limitations noted with the A1c Derived Average Glucose study.  There were a small number of ethnic groups included, and most of the subjects were Caucasian.  There were no data in children, pregnant women, or patients with renal impairment.  In addition, there was enough scatter around the hemoglobin A1c values that brings the concept of the glycation gap into the picture.  It is hypothesized that some patients are high glycators and some are low glycators.  This means although they have the same average blood glucose, the high glycator will have a much higher A1c than the low glycator.  This is notable if you examine the confidence intervals around a hemoglobin A1c of 7%, which translates to an eAG of 154 mg/dL.  The confidence intervals around the HbA1c is 6.7-9.2% and the eAG is anywhere from 123 to 185 mg/dL.  This wide margin of error has potential clinical and analytical implications for interpretation.

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• Introduction
• US Diabetes Prevalence
• Diagnosis of Diabetes
• Categories of Glucose Values
• Importance of Diagnosis
• Role of the Laboratory
• Fasting Plasma Glucose
• Fasting Plasma Glucose
• Hemoglobin A1c (HbA1c)
• Glycation
• HbA1c Concentration
• Diabetes Treatment Goals
• HbA1c Methods
• Hemoglobin Variants
• Hemoglobinopathies
• Reporting HbA1c as an eAG
• HbA1c and Average Glucose
• Derivation of Estimated Average Glucose (eAG)
• HbA1c/eAG Table
• Limitations
• Endorsement of eAG
• HbA1c for Diagnosis of Diabetes
• Disadvantages
• International Expert Committee Report on the Role of the A1c Assay in the Diagnosis of Diabetes
• HbA1c at Mayo Clinic
• Conclusions
• Questions?