The blood glucose test may be used to:
- Detect high blood glucose (hyperglycemia) and low blood glucose (hypoglycemia)
- Screen for diabetes in people who are at risk before signs and symptoms are apparent; in some cases, there may be no early signs or symptoms of diabetes. Screening can therefore be useful in helping to identify it and allowing for treatment before the condition worsens or complications arise.
- Help diagnose diabetes, prediabetes
- Monitor glucose levels in people diagnosed with diabetes
Screening and diagnosis
The following tests may be advised:
- Fasting glucose (fasting blood glucose, FBG) – this test measures the level of glucose in the blood after fasting for at least 8 hours.
- 2-hour glucose tolerance test (GTT) – for this test, the person has a fasting glucose test done (see above), then drinks a 75-gram glucose drink. Another blood sample is drawn 2 hours after the glucose drink. This protocol “challenges” the person’s body to process the glucose. Normally, the blood glucose level rises after the drink and stimulates the pancreas to release insulin into the bloodstream. Insulin allows the glucose to be taken up by cells. As time passes, the blood glucose level is expected to decrease again. When a person is unable to produce enough insulin, or if the body’s cells are resistant to its effects (insulin resistance), then less glucose is transported from the blood into cells and the blood glucose level remains high.
- A different test called hemoglobin A1c may be used as an alternative to glucose testing for screening and diagnosis.
A blood glucose test may also be ordered when someone has signs and symptoms of high blood glucose (hyperglycemia), such as:
- Increased thirst, usually with frequent urination
- Blurred vision
- Slow-healing wounds or infections
or symptoms of low blood glucose (hypoglycemia), such as:
- Blurred vision