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How to Read Your Fasting Blood Sugar Number

Here is how to make sense of a fasting blood sugar (glucose) result on a lab report.

  1. What fasting blood sugar measures

    Fasting blood sugar is measured after at least 8 hours of not eating anything except water. Because blood sugar naturally rises after any meal, measuring it in a fasted state gives a consistent baseline for comparison.

  2. Typical normal range

    Under commonly used US (ADA) guidelines, a fasting glucose below 100 mg/dL (5.6 mmol/L) is considered normal. Some other guidelines, including the World Health Organization's, place the normal cutoff slightly lower, below 110 mg/dL (6.1 mmol/L) -- so the exact cutoff your lab report uses can vary by country and by which reference range the lab applies.

  3. The 'prediabetes' range

    Under ADA criteria, a fasting glucose of 100-125 mg/dL (5.6-6.9 mmol/L) is classified as impaired fasting glucose, commonly called prediabetes. WHO-based criteria, used in many other countries, generally place this range at 110-125 mg/dL (6.1-6.9 mmol/L) instead. Either way, it is not yet a diabetes diagnosis, but it is a range where lifestyle changes are commonly recommended to reduce the risk of progressing to diabetes.

  4. The diabetes diagnostic threshold

    A fasting glucose of 126 mg/dL (7.0 mmol/L) or higher raises suspicion of diabetes under most major guidelines. A diagnosis is usually confirmed with a repeat test on a different day, or by checking it alongside another measure like HbA1c, rather than from a single reading alone.

  5. Why HbA1c is often checked alongside it

    HbA1c reflects average blood sugar over roughly the past two to three months. Under ADA reference ranges, below 5.7% is considered normal, 5.7-6.4% is prediabetes, and 6.5% or higher is diabetes (some other guidelines, such as those used in the UK, set the prediabetes band slightly differently, around 6.0-6.4%). Because a single fasting glucose reading can be affected by that day's condition, pairing it with HbA1c gives a more stable overall picture.

  6. What to do if your number is in the borderline range

    When fasting glucose or HbA1c falls in the prediabetes range, lifestyle changes -- weight management, more fiber in the diet, and regular exercise -- are reported to bring some people back into the normal range. That said, the right management plan and whether medication is needed should always be decided together with a doctor, since it depends on your individual health picture.

Guideline numbers vary a bit by country

The exact mg/dL or mmol/L cutoffs for 'normal,' 'prediabetes,' and 'diabetes' are not identical worldwide -- the American Diabetes Association, the World Health Organization, and various national health bodies each publish their own reference ranges, which are broadly similar but not always numerically identical. If your result sits near a boundary, ask your own clinician which reference range your lab report is using.

A prediabetes result is often reversible with early action

Impaired fasting glucose is not yet diabetes, but leaving it unmanaged raises the risk of it progressing. On the other hand, some people who manage their weight and eating habits during this stage do return to the normal range, which is one reason a prediabetes result is worth taking seriously rather than dismissing as a minor finding. This page provides general information about interpreting a fasting blood sugar result and is not a medical diagnosis -- consult a doctor if your numbers are concerning.

Frequently Asked Questions

My fasting glucose came back over 126 mg/dL once -- does that mean I have diabetes?

Not necessarily from a single reading. It is standard practice to confirm with a repeat test on a different day, or alongside another measure like HbA1c, before finalizing a diabetes diagnosis.

Does eating late the night before a fasting blood test affect the result?

Yes. A fasting blood sugar test assumes at least 8 hours without food, so eating within that window can push the reading higher than your true baseline -- confirm the fasting requirement before your test and follow it as closely as you can.