Fasting glucose is the amount of sugar in your blood after 8 or more hours without food. It is the most common metabolic test there is — and also one of the most over-interpreted, because it is a single snapshot.
Check your value
Reference range used: 70–99 mg/dL. Runs in your browser — nothing is stored.
mg/dL
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Wellness information, not medical advice. Reference ranges vary between laboratories and depend on age, sex and context. This page cannot diagnose anything — always read your result with the range printed on your own report, and discuss concerns with a doctor.
A result sits where it does because of the previous evening's meal, how you slept, whether you are unwell, and how stressed you were in the waiting room. One borderline reading is not a conclusion.
Why it matters
Fasting glucose is a late marker. Insulin resistance typically develops years before fasting glucose moves, because the body compensates by producing more insulin to keep glucose in range.
What influences your fasting glucose
Sleep — one poor night measurably reduces insulin sensitivity the next morning.
Acute stress or illness, which raises cortisol and with it glucose.
The previous evening's meal, particularly if late and carbohydrate-heavy.
The dawn phenomenon, a normal early-morning hormonal rise in glucose.
What to do with the result
Never conclude anything from one borderline result. Repeat it, ideally alongside HbA1c, which is far less volatile.
If fasting glucose is normal but triglycerides are high, insulin resistance can still be present — which is what markers like the TyG index are for.
Movement after meals and consistent sleep are the two habits with the clearest effect on this marker.
Common questions
What is a normal fasting glucose?
Commonly used ranges are: normal below 100 mg/dL (5.6 mmol/L), prediabetes 100–125 mg/dL (5.6–6.9 mmol/L), and diabetes at 126 mg/dL (7.0 mmol/L) or above on repeated testing.
My result is in mmol/L — how do I convert?
Multiply mmol/L by 18 to get mg/dL. So 5.6 mmol/L is about 100 mg/dL.
Can stress alone raise it?
Yes. Cortisol raises blood glucose, so illness, poor sleep or acute stress can push a reading up by a clinically meaningful amount without any underlying metabolic problem.
Is fasting glucose or HbA1c more useful?
They answer different questions. Glucose is today; HbA1c is the last three months. Read together they are far more informative than either alone.
See this marker in context
A single value tells you little on its own. PhisBio Lab reads your whole blood panel and shows how five body systems — including Metabolism — are doing together.