Normal Hemoglobin A1c Values
In individuals without diabetes, the normal hemoglobin A1c range is below 5.7%, with laboratory reference intervals typically falling between 4.0-5.2% to 5.5-5.9%. 1, 2
Defining Normal A1c Ranges
The American Diabetes Association establishes clear glycemic categories based on A1c values 1:
- Normal (non-diabetic): A1c below 5.7%
- Prediabetes: A1c 5.7-6.4%
- Diabetes: A1c ≥6.5%
Laboratory-specific reference intervals from validated chromatographic assays demonstrate normal ranges of 4.0-5.2%, with some variation depending on the measurement method used 2. Early research using high-performance liquid chromatography found normal control groups had mean A1c values of 5.6-7.1% across different age strata 3.
Clinical Significance of the 5.7% Threshold
The 5.7% cutpoint represents the lower boundary where diabetes risk begins to substantially increase. Individuals with A1c between 5.5-6.0% have a 5-year cumulative diabetes incidence of 12-25%, which is three- to eightfold higher than the general U.S. population 1. Those with A1c 6.0-6.5% face even greater risk, with 5-year diabetes incidence of 25-50% and relative risk 20 times higher compared to A1c of 5.0% 1, 4.
Important Caveats About "Normal" A1c
The continuum of diabetes risk extends well into the statistically "normal" range, meaning there is no absolute safe threshold. Even A1c values above the laboratory normal range but below 5.7% carry elevated risk compared to lower values 1.
Linear regression analyses from NHANES data indicate that a fasting plasma glucose of 100 mg/dL corresponds to an A1c of approximately 5.4%, while 110 mg/dL corresponds to 5.6% 1. This demonstrates that metabolic abnormalities can exist even when A1c remains in the "normal" range.
Age-specific considerations matter: In youth and early adolescence, only 2% of normal-weight individuals have A1c ≥5.7%, suggesting that adult prediabetes criteria should be applied cautiously in pediatric populations 5.
Practical Application
For screening purposes, an A1c below 5.5% effectively excludes diabetes, while values above 6.2% strongly suggest diabetes 2. However, any A1c value above 5.5% warrants clinical attention for diabetes prevention strategies, particularly when combined with other risk factors such as obesity, family history, or cardiovascular disease risk 1, 4.