HbA1c to Average Blood Glucose Conversion
An HbA1c of 6.0% corresponds to an estimated average blood glucose of approximately 126 mg/dL (7.0 mmol/L). 1
The Mathematical Relationship
The conversion from HbA1c percentage to average blood glucose follows a well-established linear relationship derived from the Diabetes Control and Complications Trial (DCCT):
- Each 1% increase in HbA1c corresponds to approximately 35 mg/dL (2 mmol/L) increase in mean plasma glucose 1
- An HbA1c of 6% specifically equals a mean plasma glucose of 135 mg/dL (7.5 mmol/L) 1
Calculation Formula
Using the regression equation established by Nathan and colleagues from the DCCT data, you can calculate estimated average glucose (eAG) from any HbA1c value 2. The formula provides:
- HbA1c 5% = ~100 mg/dL
- HbA1c 6% = ~135 mg/dL
- HbA1c 7% = ~170 mg/dL
- HbA1c 8% = ~205 mg/dL
- HbA1c 9% = ~240 mg/dL
Each percentage point represents approximately 35 mg/dL difference 1.
Clinical Context for 6.0%
An HbA1c of 6.0% falls within the prediabetes range (5.7-6.4%) as defined by the American Diabetes Association 1. This level:
- Indicates high risk for developing future diabetes 1
- Reflects average glucose exposure over the preceding 60-90 days 1
- Represents borderline glycemic control requiring intervention 1
Important Caveats
The HbA1c does not reflect blood glucose equally over the previous 120 days 1. The weighting is:
- 50% from the most recent month
- 25% from 30-60 days prior
- 25% from 60-120 days prior 1
Certain conditions can affect the accuracy of HbA1c-to-glucose correlation 3:
- Chronic kidney disease significantly weakens the correlation between HbA1c and actual glucose levels 3
- Anemia (hemoglobin <130 g/L in men, <120 g/L in women) reduces reliability 3
- Hemoglobin variants (S, C, and over 700 other variants) can cause spuriously high or low results 1
The eAG and random blood glucose values cannot be used interchangeably, despite both being expressed in mg/dL 2. The eAG represents an average over months, while random glucose is a single point-in-time measurement 2.