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Blood glucose test

Blood glucose tests are also sometimes called blood sugar tests. They can be done as a fasting sample or as a test called an oral glucose tolerance test. They are usually used to check for or monitor diabetes.

What is being tested?

This test measures the amount of glucose in your blood. Glucose is a simple sugar that provides energy for the body.

People with diabetes often monitor their own blood glucose at home. This is done using a finger-prick test and a special machine, rather than a blood sample taken from a vein.

You might have blood taken for a blood sugar level. You might or might not be asked to fast beforehand.

There is also a particular test called an oral glucose tolerance test, abbreviated as OGTT or GTT. For this test you fast, then have a blood sample taken, then drink glucose, then have a number of samples taken over a few hours.

Why would I need this test?

You might need this test if you are at risk of developing diabetes, or if you have had any symptoms or test results suggesting diabetes.

The standard blood glucose tests measure your blood sugar level at a particular time. The OGTT measures how you respond to glucose.

Pregnant women can develop a particular type of diabetes called gestational diabetes, and might be asked to have an OGTT around 28 weeks of pregnancy. Gestational diabetes usually goes away after the baby is born.

How to prepare for this test

If you’re asked to fast, you can’t eat anything for 8-10 hours before the test. You should drink only water.

If you are having an OGTT, you will need to drink a glucose drink provided after your fasting test, then stay for an additional few hours for further testing.

Understanding your results

High levels of glucose can indicate diabetes or being at risk of diabetes. There are other conditions that can also cause high glucose levels. You will need to discuss with your doctor what the test results mean for you, given your specific circumstances.

More information

About blood glucose testing

Visit Lab Tests Online website for more information about blood glucose testing.

About blood testing

Visit our ‘Guide to blood testing’ to learn more about blood tests in general with information such as:

  • what to consider before having the test
  • what happens during a blood test
  • results accuracy
  • blood tests cost.

Last reviewed: August 2016

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