A1C and Fasting Glucose Explained: Normal, Prediabetes and Diabetes Ranges

By ValueReviewHub Editorial · Sources checked September 28, 2026 · How we review

A1C and fasting glucose are the two numbers most people see on a blood sugar lab report. Knowing what they measure, and where the cut-offs for normal, prediabetes and diabetes sit, helps you have a more useful conversation with your doctor. It also helps you see through supplement marketing that promises to “fix” your numbers. The thresholds below come from the CDC.

The official cut-offs

Test	Normal	Prediabetes	Diabetes
A1C	Below 5.7%	5.7% – 6.4%	6.5% or above
Fasting blood sugar	99 mg/dL or below	100 – 125 mg/dL	126 mg/dL or above
Glucose tolerance test (2 hours)	Below 140 mg/dL	140 – 199 mg/dL	200 mg/dL or above

A diagnosis of diabetes is usually confirmed with repeat testing. Only a clinician can diagnose prediabetes or diabetes. These numbers are for understanding your results, not for self-diagnosis.

What A1C measures

A1C (also called HbA1c or glycated hemoglobin) shows the percentage of your hemoglobin, the oxygen-carrying protein in red blood cells, that has glucose attached. Red blood cells live for a few months, so A1C reflects your average blood sugar over roughly the past three months. You don’t need to fast for it.

Because A1C depends on red blood cells, conditions that affect them, such as some anemias, hemoglobin variants, recent blood loss, pregnancy or advanced kidney disease, can make results less accurate. Your clinician may use other tests in those cases.

What fasting glucose measures

A fasting plasma glucose test measures the glucose in your blood at a single moment after at least 8 hours without food. It is a snapshot, so it can be affected by illness, stress, poor sleep or some medicines on the day of the test.

Converting A1C to average glucose

A1C can be translated into an estimated average glucose (eAG) with a widely used formula from the A1C-Derived Average Glucose study: eAG (mg/dL) = 28.7 × A1C − 46.7.

A1C	Estimated average glucose
5.0%	≈ 97 mg/dL
5.7%	≈ 117 mg/dL
6.0%	≈ 126 mg/dL
6.5%	≈ 140 mg/dL
7.0%	≈ 154 mg/dL
8.0%	≈ 183 mg/dL

What to do if you’re in the prediabetes range

Prediabetes is common, and it is not inevitable that it will become type 2 diabetes. The landmark Diabetes Prevention Program trial found that a structured lifestyle program focused on modest weight loss and regular physical activity reduced the incidence of type 2 diabetes by 58% over an average of 2.8 years, compared with a 31% reduction for the drug metformin. Practical next steps:

Ask your clinician how often to retest and whether other tests are needed.
Ask about a recognized lifestyle-change program in your area.
Focus on the basics: regular activity, fiber-rich foods, fewer sugary drinks, adequate sleep and, if needed, weight loss.
Be cautious with supplements. Most have weak or mixed evidence. See our guides to berberine, chromium and cinnamon.

Warning signs that need prompt care

Seek medical care promptly for extreme thirst, frequent urination, unexplained weight loss, blurred vision, or confusion, vomiting or rapid breathing, which can be signs of dangerously high blood sugar. If you use insulin or other glucose-lowering medicines, learn the symptoms of low blood sugar as well: shakiness, sweating, confusion and fast heartbeat.

FAQ

Can I lower my A1C with supplements alone?

There is no strong evidence that any supplement reliably lowers A1C enough to replace lifestyle changes or medication. Berberine has the most trial data, and its effect is moderate.

How often should A1C be checked?

It depends on your results and treatment. Your clinician will recommend a schedule.

Sources

Medical note: This article is general education, not medical advice. Talk to your doctor or pharmacist before starting a supplement, especially if you take medication, are pregnant or breastfeeding, or have a health condition. Read our medical disclaimer.