Relationship Between Average Blood Glucose Level of 108 mg/dL and HbA1c
An average blood glucose level of 108 mg/dL corresponds to an HbA1c of approximately 5.3%. 1
Understanding the Relationship Between Blood Glucose and HbA1c
HbA1c reflects the average blood glucose levels over the previous 2-3 months, with recent glycemic control having a greater influence on the value:
- Approximately 50% of HbA1c is determined by glycemia during the 1 month preceding the measurement 1
- About 25% reflects glycemia from 30-60 days before measurement 1
- The remaining 25% reflects glycemia from 60-120 days prior to measurement 1
Conversion Formula Based on DCCT Data
The relationship between average blood glucose and HbA1c follows these patterns:
- An HbA1c of 6% corresponds to a mean plasma glucose level of approximately 135 mg/dL (7.5 mmol/L) 1
- Each 1% increase in HbA1c corresponds to an increase in mean plasma glucose of approximately 35 mg/dL (2 mmol/L) 1
Using this established conversion from the Diabetes Control and Complications Trial:
- For an average blood glucose of 108 mg/dL, which is approximately 27 mg/dL lower than the 135 mg/dL corresponding to an HbA1c of 6%, the equivalent HbA1c would be approximately 5.3% 1
Clinical Context
This HbA1c value of 5.3% has the following clinical implications:
- It falls within the non-diabetic reference range of 4.5-5.6% 1
- It is below the threshold for prediabetes (5.7-6.4%) 1
- It indicates excellent glycemic control if the person has diabetes 1
Limitations of the HbA1c-Blood Glucose Relationship
Several factors can affect the relationship between HbA1c and average glucose:
- Hemoglobin variants can interfere with HbA1c measurements, causing falsely high or low results 1
- Conditions that shorten red blood cell lifespan (hemolytic anemia, blood loss) can falsely lower HbA1c values 1
- Small changes in HbA1c (±0.3%) may reflect assay variability rather than true changes in glycemic status 1
Importance of Standardized Testing
For accurate interpretation:
- Use NGSP-certified methods for HbA1c testing to ensure reliability 1
- Be aware that the correlation between HbA1c and average glucose is strongest when using continuous glucose monitoring data over 8-12 weeks 2
- Consider that random blood glucose measurements and estimated average glucose calculated from HbA1c cannot be used interchangeably, though they show strong correlation in diabetic populations 3