Glucose Fasting Test

A fasting blood sugar test measures sugar (glucose) in your blood. It's a simple, safe and common way to diagnose prediabetes, diabetes or gestational diabetes. A healthcare provider will prick your finger or use a needle to draw blood from a vein in your arm.

Fasting blood sugar is a simple, common blood test to screen for diabetes, prediabetes or gestational diabetes (during pregnancy). It’s also called a fasting blood glucose test.

When does a person need to have their blood glucose measured with this test?

Prediabetes, Type 2 diabetes and gestational diabetes often have no symptoms at first. A person can have the condition and not know it. Healthcare providers usually order a fasting blood sugar test:

• As part of a standard annual physical examination to monitor a person’s blood glucose over time.
• For pregnant women to ensure that pregnancy hormones are not causing diabetes.
• When a person has symptoms of diabetes, a family history of diabetes or risk factors for diabetes (such as obesity).
• When a person has had a previous blood glucose level that was higher than normal.

Who performs a fasting blood sugar test?

Fasting blood sugar tests occur in a doctor’s office, lab or hospital.

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How does blood glucose work?

Blood sugar, or glucose, is the main sugar found in your blood. When you eat or drink, your body breaks down carbohydrates in the food or liquid into sugar for energy.

Then your pancreas produces a hormone called insulin, which helps blood sugar enter your body’s cells. It also helps your body store blood sugar for later use. As the cells use the blood sugar, glucose and insulin levels in the blood decrease.

But with diabetes, your body has trouble regulating glucose. Either your pancreas doesn’t make enough insulin, or your body doesn’t process insulin effectively. Therefore, the amount of sugar in your blood is higher than normal. And a lot of glucose in your blood is bad for your body.

A fasting blood glucose test measures the amount of glucose in your blood when it should be at its lowest. That happens in the morning and when you haven’t had anything to eat or drink for a while.

How do I prepare for a fasting blood sugar test?

To prepare for a fasting glucose test, you should have nothing to eat or drink (except water) for 8 to 12 hours. Your healthcare provider will tell you how long to fast.