Fasting blood sugar levels: normal, prediabetes and high

A fasting blood sugar levels chart gives a quick way to understand a lab result: below 100 mg/dL (5.6 mmol/L) is normal, 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is the prediabetes range, and 126 mg/dL (7.0 mmol/L) or higher is in the diabetes range. These are diagnostic cutoffs for a lab test after at least eight hours without calories, not a diagnosis from one home meter reading. A clinician considers the full picture and usually confirms an abnormal result. ADA Standards of Care, PMID 36507649

Fasting blood sugar ranges chart

Fasting plasma glucose result	General interpretation
Below 70 mg/dL (3.9 mmol/L)	Low reading; symptoms and context matter
70 to 99 mg/dL (3.9 to 5.5 mmol/L)	Normal range
100 to 125 mg/dL (5.6 to 6.9 mmol/L)	Prediabetes range
126 mg/dL (7.0 mmol/L) or higher	Diabetes range; requires clinical confirmation

The diagnostic thresholds for normal, prediabetes and diabetes come from ADA criteria. The low range is included as a practical flag, but a value below 70 by itself does not establish a hypoglycemia disorder in someone without diabetes. ADA Standards, PMID 36507649 Non-Diabetic Hypoglycemia, PMID 34424652

The fasting test means no food or calorie-containing drinks for at least eight hours; plain water is generally permitted. The test is usually performed by a laboratory. Home meters can help track patterns when a care team recommends them, but they are not the same as a diagnostic lab test. For a comparison of test types, see glucose blood tests explained and how to check blood sugar at home.

What counts as high fasting blood sugar?

A fasting laboratory result from 100 to 125 mg/dL is called impaired fasting glucose, one definition of prediabetes. A result of 126 mg/dL or higher meets the diabetes threshold, but in a person without clear symptoms, the ADA recommends confirmation with a repeat test or another diagnostic test. Different tests can identify different people, so a fasting result and A1C do not always tell the same story. ADA Standards, PMID 36507649

A mildly elevated value is a reason to follow up, not a verdict about what will happen. A single result can be affected by preparation, illness, stress, sleep, and ordinary biological variation. In a study of people at high risk, repeat testing found that glucose status could be clarified by measuring fasting glucose and A1C again; the study supports confirmation and context, not treating any one number as definitive. Chadha et al., PMID 32812912

If your number is above range, write down whether it was a lab test or meter reading, how long you had fasted, and whether you were sick or taking medicines that could affect glucose. Ask your clinician whether to repeat it and whether an A1C or an oral glucose tolerance test is useful. Read more about prediabetes range, what an A1C of 5.7, 5.8 or 5.9 means, and A1C versus glucose.

Is there a fasting blood sugar chart by age?

For nonpregnant adults, the commonly used fasting diagnostic cutoffs do not change into separate age bands. That means a fasting blood sugar chart by age should not imply that, for example, a value in the diabetes range becomes normal simply because someone is older. Age, health conditions, medicines, and overall goals can matter when a clinician interprets results or sets treatment targets for a person already diagnosed with diabetes, but those are individual care decisions. The standard diagnostic categories above remain the useful starting point. ADA Standards, PMID 36507649

People sometimes search for the “best fasting blood sugar level.” In the diagnostic framework, a lab value below 100 mg/dL is normal. There is no single ideal number that every healthy person must reach, and trying to drive glucose as low as possible is not a sensible goal. A clinician will consider the test method, repeated measurements, other results, and health history. Our normal blood sugar levels chart by age explains the difference between general diagnostic cutoffs and personal targets.

Fasting glucose and A1C: why both can help

Fasting glucose is a snapshot taken after an overnight fast. A1C estimates average glucose over roughly the previous two to three months, so it can add perspective when fasting numbers are borderline or inconsistent. Under ADA criteria, an A1C of 5.7% to 6.4% is in the prediabetes range and 6.5% or higher is in the diabetes range. Certain conditions that change red blood cells can affect A1C interpretation, so clinicians may rely more on plasma glucose in those situations. ADA Standards, PMID 36507649

A fasting blood sugar and A1C chart is useful as a comparison, but the measures are not interchangeable. The result from one cannot be converted into the other with certainty for an individual. If your A1C is elevated while fasting glucose is not, or vice versa, ask what follow-up fits your situation. See our A1C chart and A1C calculator for more on the two measures.

Low blood sugar levels chart: when a low deserves attention

A reading under 70 mg/dL (3.9 mmol/L) is commonly used as a low-glucose alert, especially in diabetes care. For adults without diabetes, true hypoglycemia is less common and should be assessed with symptoms and a documented low glucose reading. The clinical concept called Whipple’s triad includes compatible symptoms, low plasma glucose at the time, and relief when glucose returns to normal. A clinician can determine whether evaluation is warranted. Ahmed et al., PMID 34424652

Shaking, sweating, confusion, weakness, and fainting can have several causes, so symptoms alone do not identify low blood sugar. Confusion or fainting with a low reading needs urgent help, particularly if the person cannot safely swallow or is hard to wake. Do not give food or drink to someone who is unconscious. If a person with diabetes uses glucose-lowering medicine, follow the emergency plan from their care team. For more detail, see low blood sugar symptoms and low blood sugar without diabetes.

Habits that support healthier glucose

When a result falls in the prediabetes range, start with sustainable habits and a conversation with your clinician. In the Diabetes Prevention Program trial, a structured lifestyle program for adults at high risk set goals of at least 7% weight loss and 150 minutes of weekly physical activity; the intervention lowered diabetes incidence compared with placebo over an average 2.8 years. That trial tested a structured program in a defined population, so its results should not be read as a guarantee for any individual. Knowler et al., PMID 11832527

Practical starting points include regular walking or other activity you can maintain, meals built around vegetables, beans, whole grains and protein, and addressing excess weight gradually if appropriate for you. A clinician or registered dietitian can help tailor changes around other health needs. Avoid extreme fasting or major diet changes without medical advice, especially if you take medication that affects glucose. The DPP supports an organized lifestyle approach, rather than a quick fix. Knowler et al., PMID 11832527

Results vary. Talk to your doctor, especially with medications, before making major changes or adding a supplement. New or worsening symptoms deserve medical care. Very high glucose together with vomiting, confusion, or trouble breathing needs urgent evaluation; low glucose with confusion or fainting is urgent too.

What about supplements?

Supplements should come after testing, follow-up, and daily habits. They are not a substitute for diabetes care, and evidence for products varies. Our blood sugar supplements comparison explains how we assess labels and research; our scores are strict, and a high product score does not mean a supplement treats a disease. See the GlucoBerry review for its label-specific findings. Talk with your doctor before using supplements, especially if you take medication, because ingredients can interact or affect glucose.

Next step

If you have an elevated fasting result, the most useful next step is to understand how it fits with A1C and repeat testing. Start with A1C versus glucose and bring your results and questions to your clinician.

FAQ

Do I need to fast for exactly eight hours?

The diagnostic fasting test is taken after at least eight hours without calories. Follow the lab or clinician’s instructions about timing and water. ADA Standards, PMID 36507649

Is 110 mg/dL fasting diabetes?

No. A lab fasting result of 110 mg/dL falls in the prediabetes range. A clinician may repeat testing or use another test to understand your overall glucose status. ADA Standards, PMID 36507649

Can fasting blood sugar levels change with age?

The diagnostic thresholds for adults are not divided into age-specific categories. Personal treatment goals for someone with diabetes can differ, so ask the clinician managing your care. ADA Standards, PMID 36507649

Is a home meter enough to diagnose prediabetes?

No. A home meter can show readings, but diagnosis uses laboratory criteria and clinical confirmation where appropriate. Ask your clinician how to follow up on a pattern. ADA Standards, PMID 36507649

When is a low reading an emergency?

Low glucose with confusion, fainting, inability to swallow safely, or difficulty waking is urgent. In adults without diabetes, symptoms and a documented low value should be assessed clinically. Ahmed et al., PMID 34424652