Estimated A1C for Average Blood Glucose of 168 mg/dL
Based on the standardized conversion table from the A1C-Derived Average Glucose (ADAG) study, an average blood glucose of 168 mg/dL corresponds to an estimated A1C of approximately 7.3%.
Mathematical Relationship
The ADAG study established a strong correlation (r = 0.92) between A1C and average glucose using approximately 2,700 glucose measurements over 3 months per A1C measurement in 507 adults with type 1, type 2, and no diabetes 1, 2.
Using the validated conversion table 1:
- A1C of 7% = mean plasma glucose of 154 mg/dL
- A1C of 8% = mean plasma glucose of 183 mg/dL
Since 168 mg/dL falls between these two values, the corresponding A1C would be approximately 7.3% through linear interpolation 1.
Alternative Calculation Method
The linear regression formula from the ADAG study can also be used 2:
- Average Glucose (mg/dL) = 28.7 × A1C - 46.7
- Solving for A1C when average glucose = 168 mg/dL:
- 168 = 28.7 × A1C - 46.7
- A1C ≈ 7.5%
This slight variation reflects the mathematical approximation, but the conversion table method is the clinically recommended approach 1.
Clinical Context
An A1C of approximately 7.3% indicates:
- Above the general target of <7% for most nonpregnant adults with diabetes 1
- Below the threshold for less stringent control (<8%) that may be appropriate for patients with limited life expectancy, history of severe hypoglycemia, or extensive comorbidities 1
- Well below the level where most patients experience hyperglycemic symptoms (threshold of 8.9% for type 2 diabetes and 10.05% for type 1 diabetes) 3
Important Caveats
Conditions affecting red blood cell turnover (hemolysis, blood loss) and hemoglobin variants can cause discrepancies between A1C and actual average glucose 1, 4.
Racial/ethnic differences may exist in the A1C-glucose relationship, with some evidence suggesting African Americans may have higher A1C values for the same mean glucose concentration 4.
Individual variability means that for any given average glucose level, there is a range of possible A1C values, though the correlation remains strong at the population level 5.