Blood Glucose Tests Explained
Understanding blood glucose is important to tell if someone has diabetes, or if they are at high risk of developing type 2 diabetes in the future.
What blood tests are there?
The two main blood tests that your healthcare professional may recommend to check your blood glucose levels are HbA1c and fasting blood glucose. Both HbA1c and fasting blood glucose can diagnose diabetes, or tell us if someone is high risk for developing type 2 diabetes in the future.
HbA1c
HbA1c is a blood test that measures average blood glucose over the last 8–12 weeks. Glucose in the blood sticks to the red blood cells, making a substance called ‘glycated haemoglobin’, known as haemoglobin A1c or HbA1c for short.
Red blood cells live for about 8–12 weeks before they are replaced by new ones so the HbA1c test provides an estimate of average blood glucose over the previous 8–12 weeks. The more glucose in your blood on average during this period, the higher the HbA1c.
People with prediabetes (NDH) should be working to try to get their HbA1C into the normal range if possible (< 42mmol/mol). An HbA1c test result above 48 would indicate you have progressed to diabetes.
Fasting blood glucose
A fasting blood glucose measures your blood sugar usually after an overnight fast (not eating). A raised blood glucose after a period of fasting can be diagnostic of diabetes or suggest people may be at high risk of developing type 2 diabetes.
Oral glucose tolerance test
An Oral Glucose Tolerance Test (OGTT) is a test where you drink a sugary liquid, and then your blood sugar levels are checked to see how your body handles the sugar. An OGTT usually involves two blood tests, the first after a period fasting and the second 2 hours after a glucose drink. The results can help to understand how well your body processes sugar and can be used to diagnose diabetes or prediabetes/NDH.
Understanding your test results
The table below can help you understand your blood test results for both HbA1c or fasting blood glucose.
| Test | Normal | High risk of developing type 2 diabetes | Diabetes |
| HbA1c (mmol/mol) | 41 and below | 42 to 47 | 48 and above |
| Fasting blood glucose (mmol/L) | 5.4 and below | 5.5 to 6.9 | 7 and above |
| Blood glucose after 2-hour oral glucose tolerance test (mmol/L) | 7.8 and below | 7.9 to 11 | 11.1 and above |
How often should my blood tests be measured?
For people who are at high risk of diabetes it is generally recommended to have a repeat blood test once every year. This monitoring can keep an eye on your risk of developing type 2 diabetes, or tell you if you have developed type 2 diabetes.
Sometimes more or less frequent testing is recommended, your healthcare professional will be able to advise what is most appropriate for you.
Cutting down on carbs can improve glucose
Most people don’t realise that starch is made up of lots of sugar molecules stuck together. Foods such as rice, bread, pasta, cereals, potatoes and yams will break down in the intestine into quite large amounts of sugar. For example, a plate of rice could have about 18 teaspoons of sugar in it. This sugar enters the bloodstream and the excess energy is stored as fat.
It’s a fact: cutting back on carbohydrates will have a big impact on your blood glucose levels and your weight.
