What is a blood glucose test?

A blood glucose test, also called a blood sugar test, measures the amount of glucose (sugar) in your blood.

Glucose comes from carbohydrates in food and gives your body energy. It is absorbed into your blood after eating.

A blood glucose test may be done:

• after you have fasted (not eaten for at least 8 hours)
• without fasting (called a random or non-fasting blood glucose test)
• as part of a test called an oral glucose tolerance test (OGTT)

When is a blood glucose test used?

Blood glucose tests are usually used to check for or monitor diabetes.

Your doctor may suggest this blood test if you:

• are at risk of developing diabetes
• have symptoms of diabetes
• have had test results suggesting you may have diabetes

You may need other diabetes tests, such as the HbA1c test, if your doctor thinks you might have diabetes. This has become the most common method for checking long term sugar levels.

Your doctor may also recommend blood glucose tests if you have symptoms of low blood glucose levels.

Some people living with diabetes may self-monitor their blood sugar levels.

Where can I get a blood glucose test?

You usually need to go to a pathology collection centre. Your doctor can recommend one near you.

Sometimes, your doctor will collect blood for testing in their clinic. Blood tests are also routinely done in hospitals.

How do I prepare for a blood glucose test?

For a fasting blood glucose test, you must not eat anything for at least 8 hours before the test. You may drink only water.

There is no special preparation for a random blood glucose test.

What happens during a blood glucose test?

Blood glucose tests are usually done at a pathology collection centre. A health professional will take a sample of blood, usually from a vein in your arm. The blood will then be sent to a laboratory for testing.

If you have diabetes, you may need to check your blood glucose levels yourself. This is usually done by placing a drop of blood from a finger prick onto a test strip and using a glucose meter to measure it. Read more on how to check your blood glucose levels at Diabetes Australia.

What do my blood glucose test results mean?

Your doctor will look at your blood test results in the context of your situation and why you are having the test. They will discuss what the test results mean for you.

High blood glucose is often caused by diabetes, pre-diabetes or gestational diabetes. But there are also other conditions that can cause high and low blood glucose levels.

If your result shows a high blood glucose level, your doctor may suggest repeating the test and having other tests.

What is an oral glucose tolerance test (OGTT)?

An OGTT measures how your body responds to glucose.

When is an oral glucose tolerance test recommended?

An OGTT is sometimes used to check for type 2 diabetes and pre-diabetes.

Pre-diabetes is when blood glucose levels are higher than normal, but not high enough to diagnose type 2 diabetes.

OGTTs is the standard test to check for gestational diabetes — a type of diabetes that starts in pregnancy.

What happens during an oral glucose tolerance test?

You need to book an appointment at a pathology collection centre. It's a good idea to book your appointment in the morning because you will need to fast at least 8 hours before the test.

The test takes about 2 hours and starts with a fasting blood test to check your baseline glucose level. Then you'll be asked to drink a glucose solution over 5 minutes.

After you've had the glucose drink, you will have one or more blood tests. Tests will be done after one hour and again after another hour to see how quickly your body processes glucose. If you are pregnant, your test will be done after 2 hours.

After drinking the solution, you can't have anything else to eat or drink until the test is finished.

Resources and support

Pathology Tests Explained has information about blood glucose testing.

Diabetes Australia has information and support for people living with diabetes.

See our 'Guide to blood testing' to learn more about blood tests, including:

• what to consider before having the test
• what happens during a blood test
• how accurate results are
• blood test costs

You can also call the healthdirect helpline on 1800 022 222 (known as NURSE-ON-CALL in Victoria). A registered nurse is available 24 hours a day, 7 days a week.

Other languages

• NSW Government has information for people living with diabetes in a range of community languages.

Looking for information for Aboriginal and/or Torres Strait Islander people?

• National Diabetes Services Scheme has support for Aboriginal and/or Torres Strait Islander people to help you live well with diabetes.