Fasting Blood Sugar Levels and Diabetes Management

Normal Blood Glucose Ranges

A good fasting blood sugar level is between 70-99 mg/dL (3.9-5.5 mmol/L) for most adults without diabetes 1, 2
Fasting blood glucose less than 100 mg/dL (5.6 mmol/L) is considered normal 1, 2
Fasting blood glucose of 126 mg/dL (7.0 mmol/L) or higher on two separate occasions is diagnostic for diabetes 1, 2

Ideal fasting blood glucose is typically below 100 mg/dL (5.6 mmol/L) for people without diabetes 1
Target fasting blood glucose range is typically 80-130 mg/dL (4.4-7.2 mmol/L) for people with diabetes 3
More stringent goals of 110-140 mg/dL (6.1-7.8 mmol/L) may be appropriate for selected patients with diabetes if they can be achieved without significant hypoglycemia 3
For hospitalized patients with diabetes, a target glucose range of 140-180 mg/dL (7.8-10.0 mmol/L) is recommended 3, 4

Biological variation in fasting glucose can range from 4.8% to 6.1% within the same person on different days 5, 6
For a true fasting glucose of 100 mg/dL, normal biological variation means values could range from 87-113 mg/dL on different days 5, 6
Factors that can affect fasting blood glucose include stress and illness 3, medications (especially glucocorticoids) 3, recent food intake (improper fasting) 1, and time of day 5

Not fasting for at least 8 hours before the test can lead to inaccurate results 1
Using point-of-care glucose meters, which may be less accurate than laboratory analyzers, can lead to incorrect diagnoses 5
Failing to consider normal biological variation when interpreting a single reading can lead to misinterpretation of results 5, 6
Not confirming abnormal results with a second test on a different day can lead to incorrect diagnoses 1