A blood glucose test measures the glucose levels in your blood. Glucose is a type of sugar. It is your body's main source of energy. A hormone called insulin helps move glucose from your bloodstream into your cells. Too much or too little glucose in the blood can be a sign of a serious medical condition. High blood glucose levels (hyperglycemia) may be a sign of diabetes, a disorder that can cause heart disease, blindness, kidney failure and other complications. Low blood glucose levels (hypoglycemia) can also lead to major health problems, including brain damage, if not treated.

Other names: blood sugar, self-monitoring of blood glucose (SMBG), fasting plasma glucose (FPG), fasting blood sugar (FBS), fasting blood glucose (FBG), glucose challenge test, oral glucose tolerance test (OGTT)

Your health care provider may order a blood glucose test if you have symptoms of high glucose levels (hyperglycemia) or low glucose levels (hypoglycemia).

Symptoms of high blood glucose levels include:

• Increased thirst
• More frequent urination
• Blurred vision
• Fatigue
• Wounds that are slow to heal

Symptoms of low blood glucose levels include:

• Anxiety
• Sweating
• Trembling
• Hunger
• Confusion

You may also need a blood glucose test if you have certain risk factors for diabetes. These include:

• Being overweight
• Lack of exercise
• Family member with diabetes
• High blood pressure
• Heart disease

If you are pregnant, you will likely get a blood glucose test between the 24th and 28th week of your pregnancy to check for gestational diabetes. Gestational diabetes is a form of diabetes that happens only during pregnancy.

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. For some types of glucose blood tests, you will need to drink a sugary drink before your blood is drawn.

If you have diabetes, your health care provider may recommend a kit to monitor your blood sugar at home. The kit will include a device to prick your finger. You will use this to collect a drop of blood for testing. Read the kit instructions carefully and talk to your health care provider to make sure you collect and test your blood correctly.

You will probably need to fast (not eat or drink) for eight hours before the test. If you are pregnant and are being checked for gestational diabetes:

• You will drink a sugary liquid one hour before your blood is drawn.
• You won't need to fast for this test.
• If your results show higher than normal blood glucose levels, you may need another test, which requires fasting.

Talk to your health provider about specific preparations needed for your glucose test.

If your results show higher than normal glucose levels, it may mean you have or are at risk for getting diabetes. High glucose levels may also be a sign of:

• Kidney disease
• Hyperthyroidism
• Pancreatitis
• Pancreatic cancer

If your results show lower than normal glucose levels, it may be a sign of:

• Hypothyroidism
• Too much insulin or other diabetes medicine
• Liver disease

If your glucose results are not normal, it doesn't necessarily mean you have a medical condition needing treatment. High stress and certain medicines can affect glucose levels. To learn what your results mean, talk to your health care provider.

1. American Diabetes Association [Internet]. Arlington (VA): American Diabetes Association; c1995–2017. Checking Your Blood Glucose [cited 2017 Jul 21]; [about 4 screens]. Available from: http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/checking-your-blood-glucose.html
2. American Diabetes Association [Internet]. Arlington (VA): American Diabetes Association; c1995–2017. Gestational Diabetes [cited 2017 Jul 21]; [about 3 screens]. Available from: http://www.diabetes.org/diabetes-basics/gestational
3. American Pregnancy Association [Internet]. Irving (TX): American Pregnancy Association; c2017. Glucose Tolerance Test [updated 2016 Sep 2; cited 2017 Jul 21]; [about 4 screens]. Available from: http://americanpregnancy.org/prenatal-testing/glucose-tolerence-test/
4. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Basics About Diabetes [updated 2015 Mar 31; cited 2017 Jul 21]; [about 3 screens]. Available from: https://www.cdc.gov/diabetes/basics/diabetes.html
5. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Blood Glucose Monitoring; 2017 Jun [cited 2017 Jul 21]; [about 4 screens]. Available from: https://www.cdc.gov/diabetes/diabetesatwork/pdfs/bloodglucosemonitoring.pdf
6. Centers for Disease Control and Prevention [Internet]. Atlanta: U.S. Department of Health and Human Services; Frequently Asked Questions (FAQs) regarding Assisted Blood Glucose Monitoring and Insulin Administration [updated 2016 Aug 19; cited 2017 Jul 21]; [about 9 screens]. Available from: https://www.cdc.gov/injectionsafety/providers/blood-glucose-monitoring_faqs.html
7. Hinkle J, Cheever K. Brunner & Suddarth's Handbook of Laboratory and Diagnostic Tests. 2nd Ed, Kindle. Philadelphia: Wolters Kluwer Health, Lippincott Williams & Wilkins; c2014. Glucose Monitoring; 317 p.
8. National Cancer Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; NCI Dictionary of Cancer Terms: glucose [cited 2017 Jul 21]; [about 3 screens]. Available from: https://www.cancer.gov/publications/dictionaries/cancer-terms?search=glucose
9. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What Are the Risks of Blood Tests? [updated 2012 Jan 6; cited 2017 Jul 21]; [about 5 screens]. Available from: https://www.nhlbi.nih.gov/health/health-topics/topics/bdt/risks
10. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; What To Expect with Blood Tests [updated 2012 Jan 6; cited 2017 Jul 21]; [about 4 screens]. Available from: https://www.nhlbi.nih.gov/health/health-topics/topics/bdt/with