Sugar and metabolism · Blood

Glucose

The blood sugar at the moment of the blood draw; measured fasting, this is the test the GP uses to diagnose or rule out diabetes.

At a glance

Measured in blood
In 16 test panels
Check the preparation

Explanation

Glucose: what is measured?

Glucose is the sugar the body gets from food and uses as fuel; insulin from the pancreas makes sure the cells take up the glucose. If insulin does not work properly or there is too little of it, the blood sugar rises. The value varies throughout the day and rises after eating; that is why the fasting value matters most (at least 8 hours without eating or drinking anything except water). A non-fasting value only says something if it is clearly too high.

What can it detect?

Diabetes mellitus: fasting value of 7.0 mmol/l or higher (venous plasma), or non-fasting 11.1 mmol/l or higher
Impaired fasting glucose (6.1 to 6.9 mmol/l): a precursor stage with a higher chance of diabetes and of cardiovascular disease
Blood sugar that is too low (hypoglycemia), especially when using insulin or some diabetes medicines

Result

What does the result mean?

Glucose too high

A fasting glucose of 7.0 mmol/l or higher fits diabetes. According to the Dutch GP guideline (NHG), the diagnosis is only certain with two fasting values of 7.0 or higher on different days, or with one high value together with symptoms such as great thirst, frequent urination, weight loss or tiredness. A fasting value between 6.1 and 6.9 mmol/l is called impaired fasting glucose: not yet diabetes, but a higher chance of it. A non-fasting value in healthy people is usually below 7.8 mmol/l; only above 11.1 does it point to diabetes. A temporarily high value also occurs with stress, fever, an acute illness, after a meal or due to medicines such as prednisone. Type 2 diabetes causes no symptoms for a long time.

Glucose too low

A low glucose (below about 3.5 to 4 mmol/l) causes symptoms such as trembling, sweating, hunger, palpitations and difficulty concentrating. In people without diabetes, true hypoglycemia is rare: prolonged fasting, heavy exertion, a lot of alcohol, a liver disease, an adrenal or pituitary problem or, very rarely, an insulin-producing tumor (insulinoma) can be the cause. In diabetes it is due to insulin or some tablets. A slightly low fasting value without symptoms is usually normal. A tube that stands for a long time before the laboratory measures it can also give a falsely low result.

After an abnormal result

With a raised fasting value, the GP repeats the fasting measurement in the laboratory; with impaired fasting glucose usually after 3 months and then every year, together with the cardiovascular risk profile. With two values of 7.0 mmol/l or higher, diabetes is diagnosed and care starts in the GP practice.

Reliability

How reliable is the test?

According to the Dutch GP guideline (NHG) on type 2 diabetes mellitus, fasting glucose in venous blood is the test the GP uses to detect and diagnose diabetes; the cutoff values (normal below 6.1; impaired 6.1 to 6.9; diabetes 7.0 mmol/l or higher) follow the WHO criteria. One raised value is not yet a diagnosis: it calls for a second fasting measurement on another day. A normal fasting value does not rule out impaired glucose tolerance (a value that is too high after eating); that requires a separate test that is rarely done in practice. A non-fasting value is only useful if it is clearly above 11.1 mmol/l.

What can affect the result?

Not being fasting is the main source of error: food, sweet drinks and coffee with sugar or milk in the 8 hours before the blood draw raise the value; only water is allowed.
Stress, fever, infections, surgery, poor sleep and medicines such as corticosteroids (prednisone), some diuretics and antipsychotics temporarily raise the blood sugar.
Glucose in the tube is broken down by blood cells if the blood is not processed quickly or does not contain an inhibitor; this can give a falsely low result. Finger-prick meters have a measurement error of 10 to 15 percent; a borderline value must be confirmed in the laboratory.
The cutoff values apply to venous plasma; capillary blood (finger prick) has slightly different limits.

Preparation

Do not eat anything for 8 hours before the sample is taken and drink only water. Ideally have your blood taken in the morning before breakfast.

Who it is for

Who is the test useful for?

Useful for

According to the NHG guideline, useful with symptoms that fit diabetes (thirst, frequent urination, weight loss, recurrent bladder infections or fungal infections, tingling) and as a check every three years from age 45 with overweight (BMI 27 or higher), type 2 diabetes in parents, brothers or sisters, high blood pressure, a disturbed fat metabolism, (an increased risk of) cardiovascular disease, or a Turkish, Moroccan, Surinamese or Hindustani background (Hindustani people from age 35). After gestational diabetes: every year for the first 5 years. In young, slim people without symptoms or family history, the chance of an abnormal result is small. Measure fasting; otherwise the result is hard to interpret.

How common is it?

In 2024, about 1.2 million people in the Netherlands were known to their GP to have diabetes, of whom just over 1.1 million had type 2 (61 per 1000 inhabitants; 67 per 1000 men and 56 per 1000 women). It mainly occurs at older age: above the age of 85, about a quarter of men and a fifth of women have diabetes. According to the NHG guideline, about 30 percent of people over 60 have impaired fasting glucose or impaired glucose tolerance; at least half of them never develop diabetes.

VZinfo (RIVM) based on Nivel primary care registrations, 2024; the NHG guideline on type 2 diabetes mellitus

Drawbacks and risks

A non-fasting or a single slightly raised value can cause unnecessary worry; conversely, a normal fasting value can miss raised blood sugar after meals.

Get tested

Glucose: test panels

Glucose is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.

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Glucose
Fasting glucose; sugar metabolism.
€ 17,00
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General Health Checkup
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€ 125,00
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HOMA-IR
Calculation of insulin resistance from fasting glucose and insulin.
€ 44,00
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PhenoAge
PhenoAge Biological Age Test; determine your biological age with 9 standard blood values.
€ 85,00
Fingerstick
Glucose
Fasting glucose; sugar metabolism.
€ 17,00
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InsideTracker
InsideTracker Blood Analysis: analyze 48 biomarkers for complete health optimization and personalized recommendations.
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Keto Diet
Total cholesterol, HDL, LDL, triglycerides, glucose and HbA1c. For people on a ketogenic diet or considering starting keto.
€ 95,00
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Comprehensive Blood Test
Comprehensive blood test covering blood count, thyroid, kidney and liver function, glucose, inflammation markers and cholesterol.
€ 215,00

How reliable is the test?

Glucose