Average Blood Glucose for Each HbA1c Value
The estimated average glucose (eAG) for each HbA1c value is calculated using the formula: eAG (mg/dL) = 28.7 × HbA1c (%) - 46.7, based on the ADAG study which showed a strong correlation (r = 0.92) between HbA1c and mean glucose levels. 1
Standard Conversion Table
The American Diabetes Association provides the following equivalents between HbA1c percentages and average blood glucose levels 1, 2:
| HbA1c (%) | Average Blood Glucose (mg/dL) | Average Blood Glucose (mmol/L) |
|---|---|---|
| 5% | 97 (76-120) | 5.4 (4.2-6.7) |
| 6% | 126 (100-152) | 7.0 (5.5-8.5) |
| 7% | 154 (123-185) | 8.6 (6.8-10.3) |
| 8% | 183 (147-217) | 10.2 (8.1-12.1) |
| 9% | 212 (170-249) | 11.8 (9.4-13.9) |
| 10% | 240 (193-282) | 13.4 (10.7-15.7) |
| 11% | 269 (217-314) | 14.9 (12.0-17.5) |
| 12% | 298 (240-347) | 16.5 (13.3-19.3) |
Values in parentheses represent 95% confidence intervals 1
Key Clinical Points
Basis of These Estimates
- These estimates derive from the international ADAG study, which analyzed approximately 2,700 glucose measurements over 3 months per HbA1c measurement in 507 adults with type 1 diabetes, type 2 diabetes, and no diabetes 1, 2
- The correlation coefficient of 0.92 between HbA1c and average glucose is strong enough that the American Diabetes Association and American Association for Clinical Chemistry recommend reporting both HbA1c and eAG results together 1, 2
Important Limitations to Consider
When eAG is Unreliable:
- Conditions affecting red blood cell turnover make eAG calculations inaccurate: hemolytic anemia, other anemias, glucose-6-phosphate dehydrogenase deficiency, recent blood transfusion, erythropoiesis-stimulating drugs, end-stage kidney disease, and pregnancy 1, 2
- Hemoglobin variants can interfere with HbA1c assays, though most U.S. assays are accurate for heterozygous common variants 1
- HbA1c cannot be measured in sickle cell disease (HbSS) or other homozygous hemoglobin variants since these individuals lack HbA 1
What eAG Does NOT Tell You:
- eAG reflects only average glucose and provides no information about glycemic variability, hypoglycemia risk, or glucose excursions 1, 2
- Research shows clinically significant disagreement between eAG and actual mean blood glucose occurs in approximately 33% of patients, with eAG tending to overestimate at lower glucose levels 3
Racial and Ethnic Considerations
- African Americans may have slightly higher HbA1c values compared to non-Hispanic Whites for the same mean glucose concentration, though this remains an area of ongoing investigation 1
- Afro-Caribbeans have shown lower HbA1c relative to glucose values in some studies 1
Modern CGM Considerations
- The ADAG data are from 2008 using early CGM systems combined with capillary glucose measurements 1
- It remains unclear how generalizable these estimates are to modern CGM systems, which may differ in calibration, accuracy, lag time between interstitial and venous glucose, and wear patterns 1
Alternative Monitoring When eAG is Unreliable
- Use self-monitoring of blood glucose, continuous glucose monitoring, or glycated serum protein assays (fructosamine or glycated albumin) when conditions interfere with HbA1c interpretation 1
- For patients with significant glycemic variability, especially those with type 1 diabetes, fructosamine or glycated albumin may be more useful alternatives 1