What is it?
Glucose is the sugar that is in blood. It comes from the food and it is also made in the liver. The body must control blood glucose very carefully.
For an accurate blood glucose reading it is very important for the blood glucose to be measured after a period of fasting. Fasting means no food or calorie containing drinks consumed in the 8 to 10 hours prior to the test.
What is the healthy range?
A normal fasting blood glucose is between approximately 4 and 5.5 mmol/L.
A fasting blood glucose level of 5.6 or over could indicate insulin resistance. A fasting blood glucose level above 7.0 could indicate diabetes.
Why does it increase with insulin resistance?
Fasting blood glucose increases with insulin resistance because:
- The liver releases too much glucose into the blood.
- The body does not easily remove glucose from the blood.
- Fasting glucose can increase with exercise and stress. Where possible it is important to be mentally and physically relaxed for at least 2-3 hours prior to the test.
- A fasting blood glucose of 7.0 or more could indicate diabetes. People without a previous diagnosis of diabetes should arrange a more formal assessment with an appropriate medical professional. A fasting blood glucose of 11.0 or more in someone not known to have diabetes requires an urgent same day assessment with a medical professional.
- For people with type 1 diabetes the blood glucose is not a useful indicator of insulin resistance. So, instead of using blood glucose an approximate equivalent is to use the most recent HbA1c measurement in the % units. (HbA1c is now usually given in the mmol/mol units, the % may need to be calculated from this.)
- For people with type 2 diabetes and on medication, insulin resistance exists whatever the blood glucose reading.