Lab results explained
Fasting blood sugar normal range
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Short answer: A normal fasting blood sugar is 70 to 99 mg/dL (3.9 to 5.5 mmol/L). A result of 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is in the prediabetes range, and 126 mg/dL (7.0 mmol/L) or higher on two tests is in the diabetes range. Below 70 mg/dL is low. Your doctor confirms any diagnosis.
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Typical adult range
Your lab may print a slightly different range. Use the one on your report when there is one.
| Test | Adults |
|---|---|
| Fasting blood glucose | Low: under 70 mg/dL Normal: 70–100 mg/dL Prediabetes range: 100–126 mg/dL Diabetes range: 126 or more mg/dL |
| Post-meal glucose (2-hour) | Low: under 70 mg/dL Normal: 70–140 mg/dL Prediabetes range: 140–200 mg/dL Diabetes range: 200 or more mg/dL |
| HbA1c | Normal: under 5.7 % Prediabetes range: 5.7–6.5 % Diabetes range: 6.5 or more % |
What the fasting blood sugar test measures
Fasting blood sugar (FBS or fasting plasma glucose) measures the glucose in your blood after at least 8 hours without food or drinks other than water. It shows how well your body keeps sugar steady overnight. Results are given in mg/dL in the US, India and Pakistan, and in mmol/L in the UK and many other countries. To convert, divide mg/dL by 18. A home glucose meter reading is useful for tracking but is not used to diagnose diabetes. A lab sample from a vein is needed.
What the ranges mean
The cut-offs come from the American Diabetes Association and are widely used. A single high result is not enough for a diagnosis unless you also have clear symptoms, so doctors repeat the test or confirm it with another one. Illness, stress, steroids, poor sleep and a late meal can raise a fasting result, so a repeat on another day is common.
- Below 70 mg/dL (3.9 mmol/L): low blood sugar
- 70 to 99 mg/dL (3.9 to 5.5 mmol/L): normal
- 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
How the post-meal sugar and HbA1c fit in
Many reports also show a 2-hour post-meal (PP) sugar. Under 140 mg/dL (7.8 mmol/L) is normal, 140 to 199 is in the prediabetes range, and 200 mg/dL (11.1 mmol/L) or higher is in the diabetes range. These cut-offs were set for a formal glucose tolerance test with a 75 g glucose drink, so a PP test after an ordinary meal is a guide rather than a diagnosis. HbA1c shows your average sugar over about three months. Under 5.7% is normal, 5.7 to 6.4% is prediabetes and 6.5% or higher is in the diabetes range.
What usually happens next
If your fasting sugar is normal and you have risk factors, such as family history, extra weight around the waist or South Asian heritage, your doctor may suggest checking again every one to three years. A prediabetes result is a chance to act, as weight loss, regular activity and fewer sugary foods and refined carbohydrates can lower the risk of diabetes. If your result is in the diabetes range, your doctor will usually confirm it with a repeat test or HbA1c and then discuss a plan, which may include diet changes, exercise and medicine.
When to get help the same day
Get same-day medical care if your blood sugar is below 54 mg/dL (3.0 mmol/L), or above 400 mg/dL (22.2 mmol/L), or high with vomiting, heavy thirst and passing lots of urine. Call your local emergency number for confusion, fainting, a seizure, drowsiness that is hard to wake from, or deep fast breathing with high sugar.
Questions to ask your doctor
- Do my results mean prediabetes or diabetes, or do we need a repeat test?
- Should I have an HbA1c or a glucose tolerance test?
- What fasting sugar target should I aim for?
- Could any of my medicines be raising my blood sugar?
- How often should I get my blood sugar checked?
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More diabetes tests (3)
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Frequently asked questions
Is a fasting sugar of 110 mg/dL normal?
No. A fasting sugar of 110 mg/dL (6.1 mmol/L) is in the prediabetes range of 100 to 125 mg/dL. It does not mean you have diabetes. It is a sign to talk to your doctor about repeat testing and lifestyle steps.
Can I drink water before a fasting blood sugar test?
Yes, plain water is fine and helps the blood draw. Avoid tea, coffee, milk, juice and food for at least 8 hours. Ask your doctor whether to take your usual medicines that morning.
Why is my fasting sugar higher than my bedtime sugar?
Hormones released in the early morning can raise blood sugar before you wake, which is sometimes called the dawn phenomenon. A late snack can also play a part. If this keeps happening, show your readings to your doctor.
What is a normal fasting sugar in mmol/L?
A normal fasting sugar is 3.9 to 5.5 mmol/L. From 5.6 to 6.9 mmol/L is the prediabetes range, and 7.0 mmol/L or higher on two tests is the diabetes range.
Sources
- American Diabetes Association: Diagnosis
- MedlinePlus: Blood Glucose Test
- MedlinePlus: Hemoglobin A1C (HbA1c) Test
This page explains what results usually mean. It isn't a diagnosis or medical advice; your doctor interprets results with your symptoms, history and medicines. Medical disclaimer
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