Blood glucose test
Blood glucose tests are used to help diagnose diabetes, and to monitor blood glucose and the effect of diet and medicines on your blood glucose levels. A blood glucose test measures the amount of glucose in the blood at the time of the test.
How is the test done?
The test may be either:
- a 'fasting' blood glucose test — a fasting test is performed when you have not eaten anything for about 8 hours
- a 'random' test — in a random or non-fasting test, blood samples may be taken at any time before or after a meal.
Note: The amount of glucose in the blood rises immediately after you eat, so waiting a few hours after eating before having the random test will give glucose levels a chance to drop back down and give more accurate results.
What does it tell me?
If the random or fasting blood glucose is high, then diabetes is likely. High glucose is indicated by the following test results:
- fasting test: 7.0 millimoles [mmol] per litre [L] or higher
- random test: 11.1 mmol/L or higher.
If the blood glucose test results are borderline, then the doctor will usually order an oral glucose tolerance test before a diagnosis of diabetes can be confirmed. A borderline blood glucose test result can indicate pre-diabetes. A borderline result would be:
- fasting test: 5.5–6.8 mmol/L
- random test: 5.5–11.0 mmol/L.