In brief
Measures the glucose in your blood at the time of the test. A fasting sample or a 2-hour glucose tolerance test can help diagnose diabetes.
What it measures
The amount of glucose in your blood when the sample is taken. A glucose tolerance test starts with a fasting sample, then checks glucose 1 and 2 hours after a 75 gram glucose drink.
Why it is done
To screen for and diagnose diabetes, and to screen for gestational diabetes between weeks 24 and 28 of pregnancy.
Reading the results
- Fasting: 3.0 to 6.0 mmol/L is normal, 6.1 to 6.9 mmol/L is impaired fasting glucose, and 7.0 mmol/L or more suggests probable diabetes.
- 2 hours after the glucose drink: 3.0 to 7.7 mmol/L is normal, 7.8 to 11.0 mmol/L is impaired, and 11.1 mmol/L or more suggests probable diabetes.
- In pregnancy, a fasting result of 5.1 mmol/L or more, 10.0 or more at 1 hour, or 8.5 or more at 2 hours suggests gestational diabetes.
Reference ranges
| Result | Range |
|---|---|
| Fasting, normal glucose tolerance | 3.0 to 6.0 mmol/L |
| Fasting, impaired fasting glucose | 6.1 to 6.9 mmol/L |
| Fasting, probable diabetes | 7.0 mmol/L and above |
| Two hours after glucose drink, normal | 3.0 to 7.7 mmol/L |
| Two hours after glucose drink, impaired glucose tolerance | 7.8 to 11.0 mmol/L |
| Two hours after glucose drink, probable diabetes | 11.1 mmol/L or more |
Ranges differ between laboratories. Always compare a result with the range printed on your own report, and ask your doctor what it means for you.
Before the test
For a fasting sample, do not eat anything for 8 to 12 hours beforehand.
Units. mmol/L in Australia. US results in mg/dL can be converted with the lab units tool.
What can affect the result
- Recent food
- Some medicines
Related topics
Connections
Blood glucose (fasting) and glucose tolerance test measures
A fasting glucose of 7.0 mmol/L or more suggests probable diabetes.
A fasting glucose of 6.1 to 6.9 mmol/L is called impaired fasting glucose, above normal but below the level for diabetes.
Sources: Pathology Tests Explained, Glucose; healthdirect Australia, Pre-diabetes
Sources
Test information summarised from the sources listed on this page, read on 19 October 2026. General education only, not medical advice. Spotted a mistake? Please tell us through the HuBu-Intel contact page.