🩸 Blood Sugar
Fasting Blood Sugar Levels — Normal Ranges and What They Mean (2026)
Key Takeaways
- Normal fasting blood glucose: 3.9–5.5 mmol/L (70–100 mg/dL)
- Fasting glucose 5.6–6.9 mmol/L indicates prediabetes
- Fasting glucose 7.0 mmol/L or above on two occasions diagnoses diabetes
- Fasting means no food or drink (except water) for 8–12 hours
- HbA1c is a complementary test that shows 3-month average — not just fasting glucose
What Is Fasting Blood Sugar?
Fasting blood glucose is measured after at least 8 hours without food or caloric beverages. It reflects how well the body regulates blood glucose in the resting state — how much glucose remains in the bloodstream after overnight fasting.
3.9–5.5
mmol/L — Normal fasting glucose (UK)
5.6–6.9
mmol/L — Prediabetes range
7.0+
mmol/L — Diabetes diagnosis threshold
Complete Reference Table
| Result | UK (mmol/L) | USA (mg/dL) | Interpretation |
|---|---|---|---|
| Below 3.9 | Below 70 | Below 70 | Hypoglycaemia (low blood sugar) |
| Normal | 3.9–5.5 | 70–99 | Healthy — normal glucose regulation |
| Prediabetes | 5.6–6.9 | 100–125 | Impaired fasting glucose — act now |
| Diabetes | 7.0+ | 126+ | Diabetes (confirmed on two occasions) |
What Affects Fasting Blood Glucose
- Dawn phenomenon: Natural cortisol and growth hormone rise in early morning raises blood glucose — this is normal
- Stress: Cortisol raises blood glucose — emotional stress before a test can raise readings
- Recent illness: Infection raises blood glucose temporarily
- Medications: Steroids, beta-blockers, and some antipsychotics raise fasting glucose
Fasting Glucose vs HbA1c
These tests measure different things. Fasting glucose shows a single snapshot. HbA1c shows the 3-month average — capturing post-meal spikes that fasting glucose misses. You can have normal fasting glucose but elevated HbA1c (from post-meal spikes). Both tests together give the most complete picture of glucose regulation.
ℹ️ How to Get the Most Accurate Fasting Test
Fast for 10–12 hours (water only). Avoid intense exercise the evening before (can temporarily lower blood glucose). Do not smoke before the test. Schedule morning appointments when possible. Inform your doctor of any medications you take. Avoid testing during acute illness.⚕️ Medical Disclaimer: For informational purposes only. Not a substitute for professional medical advice.
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