Blood sugar test

Definition

A blood sugar test measures the amount of a sugar called glucose in a sample of your blood.

Glucose is a major source of energy for most cells of the body, including brain cells. Glucose is a building block for carbohydrates. Carbohydrates are found in fruit, cereal, bread, pasta, and rice. Carbohydrates are quickly turned into glucose in your body. This can raise your blood glucose level.

Hormones made in the body help control blood glucose level.

Alternative Names

Random blood sugar; Blood sugar level; Fasting blood sugar; Glucose test; Diabetic screening - blood sugar test; Diabetes - blood sugar test

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

The test may be done in the following ways:

How the Test will Feel

When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.

Why the Test is Performed

Your health care provider may order this test if you have signs of diabetes. More than likely, the provider will order a fasting blood sugar test.

The blood glucose test is also used to monitor people who already have diabetes.

The test may also be done if you have:

SCREENING FOR DIABETES

This test may also be used to screen a person for diabetes.

High blood sugar and diabetes may not cause symptoms in the early stages. A fasting blood sugar test is almost always done to screen for diabetes for all people over age 35. If you have no other diabetes risk factors, you should be tested every 3 years (more often if your weight is rising).

If you're overweight and have any of the other risk factors below, ask your provider about getting tested at an earlier age and more often:

Children age 10 and older who are overweight and have at least two of the risk factors listed above should be tested for type 2 diabetes every 3 years, even if they have no symptoms.

Normal Results

If you had a fasting blood glucose test, a level between 70 and 100 mg/dL (3.9 and 5.6 mmol/L) is considered normal.

If you had a random blood glucose test, a normal result depends on when you last ate. Most of the time, the blood glucose level will be 125 mg/dL (6.9 mmol/L) or lower.

The examples above show the common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different specimens. Talk to your provider about the meaning of your specific test results.

Blood glucose measured by a blood test from a vein is considered more accurate than blood glucose measured from a fingerstick with a blood glucose meter, or blood glucose measured by a continuous glucose monitor.

What Abnormal Results Mean

If you had a fasting blood glucose test:

If you had a random blood glucose test:

Other medical problems can also cause a higher-than-normal blood glucose level, including:

A lower-than-normal blood glucose level (hypoglycemia) may be due to:

Some medicines can raise or lower your blood glucose level. Before having the test, tell your provider about all the medicines you are taking.

For some thin young women, a fasting blood sugar level below 70 mg/dL (3.9 mmol/L) may be normal.

Risks

There is little risk involved with having your blood taken. Veins and arteries vary in size from one person to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight, but may include:

References

American Diabetes Association. 2. Classification and Diagnosis of Diabetes: Standards of Medical Care in Diabetes-2022. Diabetes Care. 2022. diabetesjournals.org/care/article/45/Supplement_1/S17/138925/2-Classification-and-Diagnosis-of-Diabetes. Accessed April 22, 2022.

US Preventive Services Task Force, Davidson KW, Barry MJ, Mangione CM, et al. Screening for prediabetes and type 2 diabetes: US Preventive Services Task Force recommendation statement. JAMA. 2021;326(8):736-743. PMID: 34427594 pubmed.ncbi.nlm.nih.gov/34427594/.


Review Date: 1/9/2022
Reviewed By: Robert Hurd, MD, Professor of Endocrinology and Health Care Ethics, Xavier University, Cincinnati, OH. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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