Normal A1C Level
A normal A1C level is below 5.7%, with values of 5.7-6.4% indicating prediabetes and 6.5% or higher on two separate occasions confirming diabetes. 1
Diagnostic Thresholds
The American Diabetes Association establishes three clear categories based on A1C values:
- Normal glycemia: A1C <5.7% 1
- Prediabetes: A1C 5.7-6.4% (39-47 mmol/mol) 1
- Diabetes: A1C ≥6.5% (48 mmol/mol) on two separate occasions 1
Understanding Risk Within the Normal Range
Even within the "normal" range below 5.7%, diabetes risk exists on a continuum:
- An A1C of 5.3% corresponds to an estimated average glucose of approximately 105 mg/dL and represents good glycemic control for individuals without diabetes 1
- Linear regression data shows that an A1C of 5.4% corresponds to a fasting plasma glucose of approximately 100 mg/dL 1
- Risk of developing diabetes increases progressively throughout the A1C spectrum, even within ranges considered normal 1
Risk Stratification for Prediabetes Range
For those in the prediabetic range, risk varies substantially:
- A1C 5.5-6.0%: Moderately increased risk with 9-25% incidence of diabetes over 5 years 1
- A1C 6.0-6.5%: Highly increased risk with 25-50% incidence over 5 years, representing a 20-fold higher relative risk compared to an A1C of 5.0% 1
Important Testing Considerations
A1C measurements for diagnosis must be performed by a clinical laboratory rather than point-of-care testing due to lack of standardization. 1
Common Pitfalls to Avoid:
- Anemia and certain medications can affect A1C accuracy, potentially leading to falsely low or high readings 1
- Very low A1C levels (<4.0%) may paradoxically indicate underlying pathology and have been associated with increased all-cause mortality in adults without diabetes 2
Screening Recommendations
For individuals with normal A1C results, the American Diabetes Association recommends: