What Is Normal Fasting Blood Glucose?

People with type 2 diabetes need to keep their blood glucose levels under control. Regular testing is usually required - and one of the tests available is a "fasting blood sugar test". This test is done to screen for diabetes (or pre-diabetes) and measures the amount of glucose (sugar) that is in the blood after you fast for at least 8 hours. What is "normal" fasting blood glucose?

• A normal range is between 70 milligrams/deciliter (mg/dl) and 100 ml/dl.
• Pre-diabetes may be present when the range is between 100 mg/dl to 125 mg/dl.
• Diabetes occurs when the blood sugar level is 126 mg/dl or higher.

Why Test Blood Glucose?

• To screen for diabetes or pre-diabetes;
• To monitor blood glucose levels in diabetics undergoing treatment, including checking for hypoglycemia (low blood sugar).

Preparing to Take the Test

You will be required to fast for at least 8 hours prior to the test, and up to 12 hours maximum. People who have to take a fasting blood glucose test will often fast overnight and then get the test done first thing in the morning. A blood sample will be drawn and sent for testing.

Factors that Can Affect the Test Result

Eating or drinking in the 8 hours before the test can affect the results. So can stress, illness, alcohol, caffeine, smoking, and certain medications.

Test Results

If your test results come back suggesting that you are either pre-diabetic or diabetic, another test will be done (on a different day). If you show signs of diabetes and the test results for both tests are similar, then it is likely that the results are correct.

Sometimes a random or casual blood glucose test is also administered. This test checks your blood glucose level at any time during the day - it doesn't matter when you last ate since blood glucose levels shouldn't normally vary too dramatically over the course of a day. If the result of this random test comes back between 140 mg/dl and 200 mg/dl, it suggests pre-diabetes. Higher than 200 mg/dl suggests diabetes. See our conversion chart for blood sugar levels to convert to mmol/L.

Remember that normal fasting blood glucose can be affected by a variety of things. Your doctor will make a diagnosis based on test results (fasting and random blood glucose tests), patient history, and symptoms.