The glucose tolerance test is used to establish person's sugar metabolism. The test establishes the body’s ability to balance blood sugar level when glucose is consumed.
Glucose tolerance test
Glucose tolerance tests are used for the diagnosis of pre-diabetes, type 2 diabetes or gestational diabetes.
More information
Check the interpretation of the glucose tolerance test in gestational diabetes screening from Womanhub (in Finnish).
To establish impaired glucose regulation (IGR) or diabetes, especially in persons belonging to risk groups.
To establish type 2 diabetes when the fasting blood sugar is between 5.6–6.9 mmol/l.
For gestational diabetes screening and post-monitoring.
For scientific research.
Following the instructions is essential for the success of the test and the interpretation of its results.
You can eat and drink normally on the days before the test, until the fast begins.
The preceding diet should contain an adequate amount of carbohydrates for at least three days.
You should avoid drinking any alcohol for 24 hours before the test.
Fasting starts 10–12 hours before the test and continues until the end of the test.
You can drink water during the fast, but do not eat or drink anything else. Do not have any sweets, cough drops, chewing gum, coffee, tea or alcohol during the test.
Do not smoke or use other nicotine products during the test.
Avoid physical exertion that makes you sweat for 24 hours before the test.
You can take necessary medication on the previous days and in the morning before the test.
The test cannot be performed during a cortisone therapy. However, the test can be performed if you use inhaled cortisone products, but take the cortisone medication only after the test.
The glucose tolerance test starts between 7–9 in the morning.
First, a sample of blood will be taken to test your fasting blood sugar level.
Directly after this, you will drink 300 ml glucose solution containing 75 gram of glucose.
When screening for gestational diabetes, new blood samples are taken 1 and 2 hours after the first sample.
In a standard glucose tolerance test, a second blood sample is taken two hours after the first.
| Blood sugar value (venous plasma) mmol/l Fasting glucose level | Blood sugar value (venous plasma) mmol/l At 2 hours |
Normal | < 6,1 | < 7,8 |
Elevated fasting glucose | 6,1 - 6,9 | < 7,8 |
Impaired glucose tolerance | < 7 | 7,8–11,0 |
Diabetes | ≥ 7 | ≥11,1 |
Glucose tolerance tests are used for many different purposes
To establish impaired glucose regulation (IGR) or diabetes, especially in persons belonging to risk groups.
To establish type 2 diabetes when the fasting blood sugar is between 5.6–6.9 mmol/l.
For gestational diabetes screening and post-monitoring.
For scientific research.
How to prepare for the glucose tolerance test
Following the instructions is essential for the success of the test and the interpretation of its results.
You can eat and drink normally on the days before the test, until the fast begins.
The preceding diet should contain an adequate amount of carbohydrates for at least three days.
You should avoid drinking any alcohol for 24 hours before the test.
Fasting starts 10–12 hours before the test and continues until the end of the test.
You can drink water during the fast, but do not eat or drink anything else. Do not have any sweets, cough drops, chewing gum, coffee, tea or alcohol during the test.
Do not smoke or use other nicotine products during the test.
Avoid physical exertion that makes you sweat for 24 hours before the test.
You can take necessary medication on the previous days and in the morning before the test.
The test cannot be performed during a cortisone therapy. However, the test can be performed if you use inhaled cortisone products, but take the cortisone medication only after the test.
How glucose tolerance test is done
The glucose tolerance test starts between 7–9 in the morning.
First, a sample of blood will be taken to test your fasting blood sugar level.
Directly after this, you will drink 300 ml glucose solution containing 75 gram of glucose.
When screening for gestational diabetes, new blood samples are taken 1 and 2 hours after the first sample.
In a standard glucose tolerance test, a second blood sample is taken two hours after the first.
Interpretation of blood sugar levels in a standard glucose tolerance test
| Blood sugar value (venous plasma) mmol/l Fasting glucose level | Blood sugar value (venous plasma) mmol/l At 2 hours |
Normal | < 6,1 | < 7,8 |
Elevated fasting glucose | 6,1 - 6,9 | < 7,8 |
Impaired glucose tolerance | < 7 | 7,8–11,0 |
Diabetes | ≥ 7 | ≥11,1 |
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Updated 7.5.2025