how long fasting for blood glucose test
1 For this test, you fast overnight, and the fasting blood sugar level is measured. 2  Then you drink a sugary liquid, and blood sugar levels are tested periodically for the next two hours. 3  A blood sugar level less than 140 mg/dL (7.8 mmol/L) is normal. A fasting blood sugar level less than 100 mg/dL (5.6 mmol/L) is normal. 2  A fasting blood sugar level from 100 to 125 mg/dL (5.6 to 6.9 mmol/L) is considered prediabetes. 3  If it's 126 mg/dL (7 mmol/L) or higher on two separate tests, you have diabetes. 4  Oral glucose tolerance test.