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Glucose (Blood)

Does this test have other names?

Blood sugar, self-monitoring of blood glucose (SMBG), fasting plasma glucose (FPG), random plasma glucose

What is this test?

A blood glucose test is a blood test that tells you if your level of glucose, or blood sugar, is within a healthy range. Fasting plasma glucose, or FPG, is a common test used to diagnose and monitor diabetes or prediabetes. 

Why do I need this test?

A healthcare provider may recommend a blood glucose test if you have symptoms of diabetes. These include increased thirst, unexplained weight loss, increased urination, tiredness, blurred vision, and sores that don't heal. Sometimes people with prediabetes or diabetes don't have any symptoms.

If you are overweight, obese, or have other risk factors for diabetes like high blood sugar, your healthcare provider may recommend this test. Other risk factors for diabetes include high blood pressure, high cholesterol, physical inactivity, and a family history of diabetes. The U.S. Preventive Services Task Force recommends that adults ages 40 to 70 who are obese or overweight have their blood glucose checked at least every 3 years as long as their results are normal. All adults should be tested for diabetes every 3 years beginning at age 45, no matter what their weight. 

If you are pregnant and have a risk of developing gestational diabetes, you may be screened frequently during and after your pregnancy. 

What other tests might I have along with this test?

Other tests that are used to diagnose diabetes or monitor blood glucose include an A1C blood test. A variation on the blood glucose test that is also sometimes used is called an oral glucose tolerance test, or OGTT. Because heart health is so closely tied to diabetes, regular checks of blood pressure, cholesterol, and triglycerides are important, too.

What do my test results mean?

A result for a lab test may be affected by many things, including the method the laboratory uses to do the test. If your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

Target blood glucose ranges vary from person to person. If you have diabetes, the American Diabetes Association's target blood glucose reading for you if you're not pregnant is between 70 and 130 milligrams per deciliter (mg/dL) before a meal. After a meal, it should be less than 180 mg/dL. Levels that are lower or higher than these may be a sign of blood sugar control problems.

For the FPG test, a level of 99 or below is normal. A level of 100 to 125 means you may have prediabetes. A level of 126 or above means you may have diabetes and need to do the test again on a different day to be sure. If you have an abnormal blood glucose, your healthcare provider may recommend behavioral counseling to help you eat better and get more exercise.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm. Your blood glucose level will be checked with this sample.

At some healthcare provider offices and when you are self-monitoring blood glucose at home, you will use a lancing device to prick your finger. Then you will collect a drop of blood on a test strip. A machine will test the drop of blood and show your blood glucose level on the meter's display panel.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my test results?

A number of factors, primarily diet, can affect blood glucose levels. Follow your healthcare provider's instructions about when to check your blood glucose and what to do before and after checking it.

How do I get ready for this test?

When your blood is drawn in an office, you typically need to fast for eight hours before the test. This means you should eat nothing and drink only water. When monitoring your blood glucose levels at home, you will often be asked to check it at different times, including before and after meals. Carefully follow your healthcare provider's instructions for checking blood glucose levels at home. 

Medical Reviewers:

  • Taylor, Wanda, RN, Ph.D.
  • Turley, Ray, BSN, MSN
  • Ziegler, Olivia W., MS, PA