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Metabolism

Glucose (Fasting)

Fasting glucose is your blood sugar after a night without eating and shows how well your body processes glucose.

What is Glucose (Fasting)?

Fasting glucose is your blood sugar level after at least eight hours of fasting. It shows how well your body processes glucose when no recent meal is complicating the picture. The value responds quickly to sleep, stress, alcohol, and the previous evening's food — more sensitive to noise than HbA1c, but also faster to respond when your lifestyle changes. For a reliable reading, test early in the morning after at least eight hours of fasting. A single measurement is rarely conclusive. Pairing it with HbA1c gives the most complete picture of glucose regulation.

Why is Glucose (Fasting) relevant?

Fasting glucose is an early signal for insulin resistance. The value starts rising while the body is still compensating — well before HbA1c moves outside the normal range. At that early stage, glucose regulation is still reversible with lifestyle change. Elevated fasting glucose alongside high triglycerides, a high triglyceride/HDL ratio, or increasing waist circumference points to an unfavourable metabolic pattern. Cardiovascular damage from chronically raised blood sugar begins in the pre-diabetes range — not only after a diabetes diagnosis is made.

Glucose (Fasting) high or low — what it means

Read fasting glucose together with HbA1c and triglycerides. Poor sleep, alcohol the evening before, and stress can all temporarily raise the value. An unexpectedly high result calls for a repeat under normal conditions. The levers for bringing elevated fasting glucose down are well established: physical activity (even short walks after meals help), limiting refined carbohydrates, losing excess weight, prioritising sleep, and managing stress. Changes are often visible within four to six weeks.

Glucose (Fasting) reference ranges

NormalFasting (≥ 8 hours), venous plasma4.0-6.0 mmol/L
Impaired fasting glucosePrediabetes range; discuss with your GP6.1-6.9 mmol/L
DiabetesConfirmed on two separate days≥ 7.0 mmol/L

Cut-offs follow the Dutch NHG guideline for type 2 diabetes and WHO criteria (fasting glucose in venous plasma): normal < 6.1; impaired fasting 6.1-6.9; diabetes ≥ 7.0 mmol/L. Values vary slightly by lab and method. A single measurement is rarely conclusive; only a clinician makes a diagnosis.

Educational information only — not medical advice. Consult a healthcare professional for clinical decisions.

Read about our scientific approach →Read the guide: Nutrition →

Frequently asked questions

What is a normal fasting glucose value?

Fasting (after at least 8 hours without food), a normal glucose value is roughly 4.0 to 6.0 mmol/L in venous plasma. A value of 6.1 to 6.9 mmol/L is called 'impaired fasting glucose' and falls in the prediabetes range. Cut-offs vary slightly between labs and methods.

What does a high fasting glucose mean?

An elevated fasting glucose (6.1-6.9 mmol/L) often points to early insulin resistance and belongs to prediabetes — an early and usually still reversible signal. A fasting value of 7.0 mmol/L or higher, confirmed on two separate days, meets the threshold for diabetes. Poor sleep, alcohol, or stress the evening before can temporarily raise a single reading, so repeat an unexpectedly high result.

What does a low fasting glucose mean?

A fasting glucose clearly below 4.0 mmol/L (hypoglycaemia) is uncommon in healthy people without diabetes and can cause symptoms such as shaking, sweating, or dizziness. A mildly low but symptom-free value is usually harmless; discuss persistently low or symptomatic values with your GP.

When is a raised fasting glucose a concern?

A one-off mild elevation is rarely cause for alarm, but a repeated impaired fasting glucose (6.1-6.9 mmol/L) or a value ≥ 7.0 mmol/L warrants attention and a check-in with your GP. Never read it in isolation: combined with a raised HbA1c, high triglycerides, or increased waist circumference it points to an unfavourable metabolic pattern. Fasting glucose is a snapshot — HbA1c gives the more stable picture over two to three months.

Related biomarkers

Hemoglobin A1c
HbA1c shows what your average blood sugar has been over the past two to three months.
Triglycerides
Triglycerides are a blood fat that responds strongly to diet and alcohol and reflects your metabolic health.
Triglycerides / HDL Ratio
The triglyceride/HDL ratio divides your triglycerides by your HDL and gives a quick read on your insulin sensitivity.

Glucose (Fasting) is one of the biomarkers in the Optimize blood test. Book a blood draw at any of 238+ partner labs in the Netherlands, or upload your existing results in the app.

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