Fasting Blood Sugar Test

What is a fasting blood sugar test?

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.

A fasting blood glucose test measures the amount of sugar in your blood when it should be at its lowest. That happens when you haven’t had anything to eat or drink for several hours (usually in the morning).

When would I need a fasting blood sugar test?

Healthcare providers usually recommend a fasting blood sugar test:

• As part of your annual physical exam and bloodwork to check blood glucose changes over time
• For pregnant women to ensure that pregnancy hormones aren’t causing diabetes
• When you have symptoms, a biological family history or risk factors for diabetes
• When you’ve had a previous blood sugar level that was higher than normal

Prediabetes, Type 2 diabetes and gestational diabetes often have no symptoms at first. You can have the condition and not know it.

How do I prepare for a fasting blood sugar test?

To prepare for a fasting blood sugar test, you shouldn’t eat or drink (except water) for eight to 12 hours before the test. Your healthcare provider will tell you exactly how long to fast.

What can I expect during the test?

A fasting blood glucose test is often done with a common blood draw. A phlebotomist will use a small needle to draw blood from a vein in your arm. After the test, they’ll send the blood sample to a lab for testing.

Sometimes, your healthcare provider may test your blood sugar with a needle prick on your finger. They’ll use a blood glucose monitor and test strip to measure your blood sugar level in the office.

When should I know the results of the test?

Results of a laboratory fasting blood sugar test are usually available quickly — within hours or days.

A finger prick test gives results within seconds.

What do the results of a fasting blood sugar test mean?

The results of the fasting blood sugar test will come back as a number:

• Less than 100 mg/dL: This is a normal fasting blood sugar level.
• 100 to 125 mg/dL: Fasting blood sugar in this range typically indicates prediabetes. This means your blood sugar levels are higher than normal but not high enough to be classified as diabetes.
• 126 mg/dL or above: This indicates high blood sugar, the main sign of diabetes.

If you live in a country other than the United States, your lab may use a different unit of measurement — mmol/L:

• Less than 5.6 mmol/L: Normal
• 5.6 to 6.9 mmol/L: Prediabetes
• 7 mmol/L or higher: Diabetes

If the results are abnormal, what are the next steps?

If you have a high fasting blood sugar level, your healthcare provider may repeat the test to make sure it was accurate. Providers don’t rely on one abnormal result to diagnose diabetes.

If the test reveals that you have prediabetes, your provider will recommend ways of getting your blood sugar into a healthy range, like with eating and physical activity changes. They’ll likely want you to get additional fasting blood sugar tests over time. The results will help you know if you’re developing Type 2 diabetes.

A fasting blood sugar of less than 70 mg/dL is considered low blood sugar for someone who has diabetes. But it may be normal for someone without diabetes. Your provider may ask if you’ve had symptoms of low blood sugar before, like shakiness. They may recommend more testing to see if this result is part of a pattern of low blood sugar episodes.