Fasting glucose
Also reported as: FPG · Fasting plasma glucose · Fasting blood sugar
Blood glucose after 8 or more hours without food.
70–99 mg/dL normal, 100–125 prediabetes, 126 or above diabetes on two occasions.
Cohort data show risk rising continuously well within the 'normal' band, with the lowest risk in the mid-70s to mid-80s.
Guideline thresholds from: American Diabetes Association Standards of Care
To convert to mmol/L, multiply by 0.0555.
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Where the thresholds sit
| Band | Range (mg/dL) | Note |
|---|---|---|
| Low | < 70 | — |
| Optimal | 75–86 | — |
| Normal | 86–100 | — |
| Prediabetes | 100–126 | — |
| Diabetes range | > 126 | — |
Why it matters
The cheapest glycaemic test, and the last one to go abnormal. The body defends fasting glucose hard, so by the time this number rises, insulin resistance has usually been present for years — which is exactly why fasting insulin is the more sensitive early marker.
What raises it
- Insulin resistance
- Acute stress, illness and poor sleep the night before
- The dawn phenomenon — a normal early-morning cortisol-driven rise
- Corticosteroids
- Low-carbohydrate diets, mildly and benignly, through physiological insulin resistance
What lowers it
- Exercise
- Weight loss
- Metformin and GLP-1 agonists
- Prolonged fasting
How to move it
- 1Retest before drawing conclusions — a single fasting glucose is noisy, and one poor night's sleep can raise it by 10 mg/dL.
- 2Ask for fasting insulin at the same time. Normal glucose with high insulin is the pattern worth catching.
- 3Post-meal walking and resistance training are the two highest-yield habits.
- 4Do not fast for longer than instructed before the test — an extended fast can raise the reading.
What moves this marker
Interventions on this site with evidence behind them for this specific marker. None of them replaces working out why yours is where it is.
What makes a single reading misleading
- Extremely sensitive to sleep, stress and the exact fasting duration.
- People eating very low carbohydrate often show mildly elevated fasting glucose with excellent HbA1c and insulin. This is adaptive, not pathological.
Sources
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Educational only. Reference ranges are not diagnostic thresholds and this page cannot account for your medical history, medication or symptoms. Discuss any result that concerns you with a qualified clinician. See our medical disclaimer.