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Diabetes Health Center

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Blood Glucose


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Many conditions can change your blood glucose levels. Your doctor will discuss any significant abnormal results with you in relation to your symptoms and past health.

For more information on results from an oral glucose tolerance test or hemoglobin A1c test, see:

High values

You may have diabetes. To make a diagnosis of type 2 diabetes, your doctor will use the American Diabetes Association's criteria.

Other conditions that can cause high blood glucose levels include:

Low values

A fasting glucose level below 40 mg/dL (2.2 mmol/L) in women or below 50 mg/dL (2.8 mmol/L) in men that is accompanied by symptoms of hypoglycemia may mean you have an insulinoma, a tumor that produces abnormally high amounts of insulin.

Low glucose levels also may be caused by:

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

  • Eating or drinking less than 8 hours before a fasting blood test or less than 2 hours before a 2-hour postprandial test.
  • Drinking alcohol on the day of the test or several days before the test.
  • Illness or emotional stress, smoking, and caffeine.
  • Taking a medicine. Make sure that your doctor knows about any medicines you take and how often you take them.

What To Think About

  • Glucose levels in urine can also be measured. Many people with diabetes have glucose in their urine. But the level in the blood must be very high before glucose can be detected in the urine. For this reason, tests for glucose in urine are not used to diagnose or monitor diabetes. To learn more, see Urine Test.
  • If you have diabetes, you will be able to measure your blood glucose levels at home. To learn more, see Home Blood Glucose Test.

WebMD Medical Reference from Healthwise

Last Updated: November 14, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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