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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?

You may need this 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, you will be screened for gestational diabetes between 24 and 28 weeks. If you have gestational diabetes, you will be checked more often during your pregnancy and again 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?

Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem. Ask your healthcare provider what your test results mean for you. 

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 is done with a blood sample. A needle is used to draw blood from a vein in your arm or hand. 

Does this test pose any risks?

Having a blood test with a needle carries some risks. These include bleeding, infection, bruising, and feeling lightheaded. When the needle pricks your arm or hand, you may feel a slight sting or pain. Afterward, the site may be 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 8 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. 

Be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illicit drugs you may use. 

Medical Reviewers:

  • Greco, Frank, MD
  • Holloway, Beth Greenblatt, RN, MEd