Blood glucose tests are also sometimes called blood sugar tests. They can be done after you have fasted 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 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 will be asked to have an OGTT around 24 to 28 weeks of pregnancy. Gestational diabetes usually goes away after the baby is born.
ARE YOU AT RISK? — Are you at risk of type 2 diabetes, heart disease or kidney disease? Use our Risk Checker to find out.
How to prepare for this test
If you’re asked to fast, you can’t eat anything for 8 to 10 hours before the test. You should drink only water.
If you are having an OGTT, you will need to adjust your diet for a few days before the test and fast for 8 hours just before the test.
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
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About blood testing
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The glucose tolerance test, also known as the oral glucose tolerance test, measures your body's response to sugar (glucose). The glucose tolerance test can be used to screen for type 2 diabetes. More commonly, a modified version of the glucose tolerance test is used to diagnose gestational diabetes — a type of diabetes that develops during pregnancy.
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Why it's done
The glucose tolerance test identifies abnormalities in the way your body handles glucose after a meal — often before your fasting blood glucose level becomes abnormal.
More Information
- Diabetes
- Dumping syndrome
- Gestational diabetes
- Polycystic ovary syndrome (PCOS)
- Prediabetes
- Type 2 diabetes
- Type 2 diabetes in children
Risks
The risks associated with obtaining a blood sample are slight. After your blood is drawn, you may experience bruising or bleeding. You may also feel dizzy or lightheaded. In some cases, infection after your procedure is possible.
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