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Fasting glucose
The glucose concentration in plasma after at least eight hours without food or caloric drinks. It is a snapshot of one morning, which is exactly its strength and its weakness: it is sensitive to what happened the night before in a way HbA1c is not.
General information only — not a diagnosis, not treatment and not a substitute for your doctor. Reference ranges differ between laboratories, so the range printed on your own report is the one that counts, and only a clinician who knows your history can say what a result means for you. Never start, stop or change a medicine or supplement based on this page.
Usual adult reference range
The ranges below are typical adult reference intervals. Your own laboratory sets its own, printed next to your result, and that is the one to compare against.
| Group | SI units (mmol/L) | Conventional (mg/dL) |
|---|---|---|
| Normal | 3.9-5.5 | 70-99 |
| Impaired fasting glucose | 5.6-6.9 | 100-125 |
| Diabetes threshold | 7.0 or above | 126 or above |
Source: Commonly used diagnostic thresholds published in clinical guidelines; laboratories print their own reference interval alongside the result. · checked 2026-09-02
What a high result generally indicates
A raised fasting glucose means the body was not holding glucose down overnight as tightly as usual. Illness, steroids, poor sleep and stress all push it up temporarily. Persistent elevation is how impaired fasting glucose and diabetes are identified — on repeated testing, by a clinician.
What a low result generally indicates
A genuinely low fasting glucose in someone not on diabetes medicine is uncommon and gets investigated. Far more often a low reading is an artefact: a sample left too long before separation lets the blood cells consume glucose, which is why laboratories use special tubes.
These are general patterns, not a diagnosis. Many things cause a high or low result, and the same figure means different things in different people. What yours means is a question for the doctor who ordered the test.
What affects this result
- Whether the fast was really a fast — milk in coffee is enough to change it.
- Acute illness, injury and surgery raise it, sometimes markedly.
- Corticosteroids raise it; so do some antipsychotics and diuretics.
- Poor or short sleep the night before raises morning glucose.
- Sample handling: delayed processing without a preservative lowers it.
- Intense exercise the previous evening can lower it the next morning.
Before the test
Eight hours or more without food or caloric drink. Water is fine.
Any preparation instruction that comes with your test slip overrides this general note — follow the one your clinician or laboratory gave you.
The one thing to take from this page
The range above is a typical interval for orientation. Your own laboratory's range, printed beside your result, is the one that applies to you — and a result is only meaningful alongside your symptoms, your history, your medicines and your other tests. That reading is a clinician's job. This page cannot diagnose anything, cannot tell you to change a medicine or a supplement, and is not a substitute for the person who ordered your test.
Frequently asked questions
What is the normal range for fasting glucose?
A typical adult reference interval is 3.9–5.5 mmol/L, but laboratories differ — the range printed on your own report is the one to use. And a result inside or outside a range is only meaningful in context, which is your doctor's reading, not a web page's.
What does a high fasting glucose mean?
A raised fasting glucose means the body was not holding glucose down overnight as tightly as usual. Illness, steroids, poor sleep and stress all push it up temporarily. Persistent elevation is how impaired fasting glucose and diabetes are identified — on repeated testing, by a clinician.
What does a low fasting glucose mean?
A genuinely low fasting glucose in someone not on diabetes medicine is uncommon and gets investigated. Far more often a low reading is an artefact: a sample left too long before separation lets the blood cells consume glucose, which is why laboratories use special tubes.
Other markers
Haemoglobin
Hb, HGB
Ferritin
Serum ferritin
Vitamin D (25-OH)
25-hydroxyvitamin D, calcidiol
HbA1c
Glycated haemoglobin, A1c
Total cholesterol
TC
LDL cholesterol
LDL-C, "bad" cholesterol
All markers and the checker · Symptoms and nutrients · Medicine interactions
Bring context to your next result
TempoLife tracks the weight, sleep and activity trends a single blood test cannot see, so you and your doctor have the fuller picture.