Glucose

Blood glucose, also known as blood sugar or GUK, is a basic test for detecting prediabetes and diabetes. It is most often measured in the morning after fasting and shows the sugar level at the time of blood collection. It is performed in preventive examinations, for symptoms suggesting high or low sugar, and to monitor diabetes.

Who is this test for

• people attending a regular preventive or general health check;
• people with increased thirst, frequent urination, fatigue, unexplained weight loss, frequent infections or slow-healing wounds;
• people at increased risk of type 2 diabetes: excess body weight, a family history of diabetes, high blood pressure or elevated blood fats;
• women with a history of gestational diabetes;
• people with repeated episodes of sweating, trembling, palpitations and intense hunger, which may indicate low sugar;
• people with diabetes or prediabetes, for monitoring.

What blood glucose shows

Glucose is the main source of energy for cells. After a meal its blood level rises, and the pancreas secretes insulin, which allows glucose to enter cells and brings the level back towards normal. When there is insufficient insulin or cells respond less well, glucose remains elevated. This is first seen after meals and later during fasting as well.

Glucose shows the situation at one moment and may vary from day to day. The average over the previous two to three months is shown by HbA1c, while how the body handles a larger amount of sugar is shown by the glucose tolerance test.

Panels including this test

Test Glucose is also included in this panel.

General preventive panelCBC, glucose, cholesterol, HDL and LDL cholesterol, triglycerides and 430.00€Details ›

All panels including Glucose (11) ›

Preparation and sample

• The sample is blood from a vein. Attend in the morning after fasting: do not eat for 8 to 12 hours before collection. Longer fasting is unnecessary.
• You may drink plain water, but avoid coffee, tea, juice and chewing gum until after collection.
• Avoid alcohol and exhausting exercise the day before, and do not smoke that morning.
• State which medicines you take when your blood is drawn: some, such as corticosteroids, raise glucose.
• If you are treated for diabetes, agree with your doctor how to take treatment on the collection day, and bring something to eat afterwards.

Acute illness, injury or severe stress may temporarily raise glucose, so results obtained in such circumstances are usually repeated.

How results are interpreted

For fasting venous blood glucose in adults other than pregnant women, the following World Health Organization (WHO) thresholds apply:

Fasting glucose	Meaning
below 6,1 mmol/L	normal
6,1–6,9 mmol/L	impaired fasting glucose (prediabetes)
7,0 mmol/L or above	diabetes, if confirmed

The American Diabetes Association (ADA) uses the same diabetes threshold but defines impaired fasting glucose from 5,6 mmol/L, so this threshold may appear on some reports and in the literature. The reference interval is printed on your report and depends on method and age; in adults it is usually around 4,4–6,4 mmol/L. For assessing prediabetes and diabetes, however, the doctor uses the table thresholds, so even a value within the interval, such as 6,2 mmol/L, may indicate impaired fasting glucose.

Diagnosing diabetes without pronounced symptoms requires two elevated results, for example repeated fasting glucose, or glucose and HbA1c. Glucose of 11,1 mmol/L or above measured at any time of day, with typical symptoms, is sufficient for diagnosis. For a borderline result, the doctor usually requests HbA1c or a glucose tolerance test.

Low glucose in people without diabetes is rare. Hypoglycaemia is identified when glucose is low with typical symptoms that stop after eating; a doctor then investigates the cause. In people treated with insulin or certain diabetes tablets, glucose below 3,9 mmol/L is low and below 3,0 mmol/L is significant hypoglycaemia.

Lower thresholds apply in pregnancy, as described under glucose tolerance testing in pregnancy. The doctor interprets results alongside symptoms, other findings and risk factors.

Glucose meter or laboratory

A glucose meter measures capillary blood glucose from a finger prick and is used for self-monitoring by people being treated for diabetes. It is not sufficiently accurate for diagnosis, which is therefore based on laboratory measurement of venous blood glucose.

How to arrange testing

You can come for blood collection without an appointment or referral at one of our branches throughout Croatia (listed on the Contact). Attend in the morning after fasting. Prices for all tests and panels are in the service price list. Glucose can also be measured with HbA1c in the Glycaemic status panel.

Frequently asked questions

What is normal fasting glucose?

In adults, normal fasting venous glucose is below 6,1 mmol/L, and below 5,6 mmol/L according to the ADA. The reference interval printed on adult reports is usually around 4,4–6,4 mmol/L, so a result within it may exceed the prediabetes threshold. A doctor makes the diagnosis according to guidelines.

What does fasting glucose of 6,5 mmol/L mean?

This is impaired fasting glucose, a form of prediabetes. It is not diabetes, but the risk is increased. The doctor will usually request HbA1c or a glucose tolerance test and suggest dietary changes, more activity and losing excess weight.

Can stress raise blood sugar?

Yes. Severe stress, acute illness, injury or fever increase hormones that raise glucose. If a result obtained in such circumstances is elevated, it is usually repeated after recovery.

Do I need to fast for glucose testing?

Yes, for detecting prediabetes and diabetes, because the thresholds refer to fasting glucose. If you ate before collection, mention this when your blood is drawn: post-meal glucose cannot be compared with these thresholds, so it is best to repeat the test another morning after fasting.